Windows does not provide a system notification the embedder can
subscribe to to determine when a screen reader or other assistive
technology that requires the semantics tree has been enabled. [1]

In the absence of such a notification, we watch for queries for the
IAccessible COM object representing the root node of the semantics tree,
and on receipt of such queries we enable the semantics tree. For the
time being, we assume that if accessiblity is enabled, it will be
enabled for the duration of the application lifetime. In a future patch
we can optimise this by adopting the approach taken by Chromium, which
is to disable semantics if we haven't received a query within some
reasonable timeout.

This patch enables Flutter's semantics tree; a follow-up patch wires in
the AccessibilityBridge which maintains the AXTree of COM objects that
is the Windows representation of the Flutter SemanticsTree.

Issue: flutter/flutter#77838

[1]: https://docs.microsoft.com/en-us/windows/win32/winauto/screen-reader-parameter

Adds method for dispatching a semantics action received from the OS to
the matching node in Flutter's semantics tree.

Issue: flutter/flutter#77838

Adds method for dispatching a semantics action received from the OS to
the matching node in Flutter's semantics tree.

Issue: flutter/flutter#77838

Adds method for dispatching a semantics action received from the OS to
the matching node in Flutter's semantics tree.

Issue: flutter/flutter#77838

Adds method for dispatching a semantics action received from the OS to
the matching node in Flutter's semantics tree.

Issue: flutter/flutter#77838

Adds method for dispatching a semantics action received from the OS to
the matching node in Flutter's semantics tree.

Issue: flutter/flutter#77838

Adds method for dispatching a semantics action received from the OS to
the matching node in Flutter's semantics tree.

Issue: flutter/flutter#77838

Windows does not provide a system notification the embedder can
subscribe to to determine when a screen reader or other assistive
technology that requires the semantics tree has been enabled. [1]

In the absence of such a notification, we watch for queries for the
IAccessible COM object representing the root node of the semantics tree,
and on receipt of such queries we enable the semantics tree. For the
time being, we assume that if accessiblity is enabled, it will be
enabled for the duration of the application lifetime. In a future patch
we can optimise this by adopting the approach taken by Chromium, which
is to disable semantics if we haven't received a query within some
reasonable timeout.

This patch enables Flutter's semantics tree; a follow-up patch wires in
the AccessibilityBridge which maintains the AXTree of COM objects that
is the Windows representation of the Flutter SemanticsTree.

Issue: flutter/flutter#77838

[1]: https://docs.microsoft.com/en-us/windows/win32/winauto/screen-reader-parameter

Windows does not provide a system notification the embedder can
subscribe to to determine when a screen reader or other assistive
technology that requires the semantics tree has been enabled. [1]

In the absence of such a notification, we watch for queries for the
IAccessible COM object representing the root node of the semantics tree,
and on receipt of such queries we enable the semantics tree. For the
time being, we assume that if accessiblity is enabled, it will be
enabled for the duration of the application lifetime. In a future patch
we can optimise this by adopting the approach taken by Chromium, which
is to disable semantics if we haven't received a query within some
reasonable timeout.

This patch enables Flutter's semantics tree; a follow-up patch wires in
the AccessibilityBridge which maintains the AXTree of COM objects that
is the Windows representation of the Flutter SemanticsTree.

Issue: flutter/flutter#77838

[1]: https://docs.microsoft.com/en-us/windows/win32/winauto/screen-reader-parameter

Adds method for dispatching a semantics action received from the OS to
the matching node in Flutter's semantics tree.

Issue: flutter/flutter#77838

Windows does not provide a system notification the embedder can
subscribe to to determine when a screen reader or other assistive
technology that requires the semantics tree has been enabled. [1]

In the absence of such a notification, we watch for queries for the
IAccessible COM object representing the root node of the semantics tree,
and on receipt of such queries we enable the semantics tree. For the
time being, we assume that if accessiblity is enabled, it will be
enabled for the duration of the application lifetime. In a future patch
we can optimise this by adopting the approach taken by Chromium, which
is to disable semantics if we haven't received a query within some
reasonable timeout.

This patch enables Flutter's semantics tree; a follow-up patch wires in
the AccessibilityBridge which maintains the AXTree of COM objects that
is the Windows representation of the Flutter SemanticsTree.

Issue: flutter/flutter#77838

[1]: https://docs.microsoft.com/en-us/windows/win32/winauto/screen-reader-parameter

This is the third in a series of patches adding accessibility support
for the Windows embedder. This patch wires in the Accessibility bridge,
and lands the core structure of the Windows FlutterPlatformNodeDelegate
and AccessibilityBridgeDelegate classes, including:

* Instantiating the AccessibilityBridge when the semantics tree is
  enabled.
* Creating FlutterPlatformNodeDelegate wrappers for semantics tree
  nodes.
* Building and updating the accessibility tree on semantics updates.
* Returning the native IAccessible objects when queried.

Breaking this out so that the follow-up patches can be reviewed and
landed in smaller, independent chunks.

Issue: flutter/flutter#77838

This is the third in a series of patches adding accessibility support
for the Windows embedder. This patch wires in the Accessibility bridge,
and lands the core structure of the Windows FlutterPlatformNodeDelegate
and AccessibilityBridgeDelegate classes, including:

* Instantiating the AccessibilityBridge when the semantics tree is
  enabled.
* Creating FlutterPlatformNodeDelegate wrappers for semantics tree
  nodes.
* Building and updating the accessibility tree on semantics updates.
* Returning the native IAccessible objects when queried.

Breaking this out so that the follow-up patches can be reviewed and
landed in smaller, independent chunks.

Issue: flutter/flutter#77838

This is the third in a series of patches adding accessibility support
for the Windows embedder. This patch wires in the Accessibility bridge,
and lands the core structure of the Windows FlutterPlatformNodeDelegate
and AccessibilityBridgeDelegate classes, including:

* Instantiating the AccessibilityBridge when the semantics tree is
  enabled.
* Creating FlutterPlatformNodeDelegate wrappers for semantics tree
  nodes.
* Building and updating the accessibility tree on semantics updates.
* Returning the native IAccessible objects when queried.

Breaking this out so that the follow-up patches can be reviewed and
landed in smaller, independent chunks.

Issue: flutter/flutter#77838

This is the third in a series of patches adding accessibility support
for the Windows embedder. This patch wires in the Accessibility bridge,
and lands the core structure of the Windows FlutterPlatformNodeDelegate
and AccessibilityBridgeDelegate classes, including:

* Instantiating the AccessibilityBridge when the semantics tree is
  enabled.
* Creating FlutterPlatformNodeDelegate wrappers for semantics tree
  nodes.
* Building and updating the accessibility tree on semantics updates.
* Returning the native IAccessible objects when queried.

Breaking this out so that the follow-up patches can be reviewed and
landed in smaller, independent chunks.

Issue: flutter/flutter#77838

This enables unittests for the accessibility bridge in
common_cpp_unittests, when running on Windows. Previously, we only
tested on macOS.

Issue: flutter/flutter#77838

In the Win32 accessibility tree, each AXTree node has an associated
IAccessible object. In WindowWin32, our WM_GETOBJECT handler returns the
IAccessible associated with the root node of the tree (node 0). On other
platforms, we often add our root accessibility object as a subnode of
some existing accessibility object associated with the view. On Windows,
the root IAccessible _is_ the accessibility object associated with the
view (on Windows, and HWND).

In the previous implementation, AccessibleObjectFromWindow actually just
returns the root IAccessible object, which is equivalent to just
returning GetNativeViewAccessible. Instead, we just return null once we
hit the root of the tree.

Issue: flutter/flutter#77838

The default implementation of GetUniqueId on ui::AXPlatformNodeDelegate
always returns ID 1. We had previously implemented this on the windows
platform node delegate, but for consistency's sake, and because the
default implementation is surprising, we're promoting this to the
FlutterPlatformNodeDelegate base class.

Issue: flutter/flutter#77838

The default implementation of GetUniqueId on ui::AXPlatformNodeDelegate
always returns ID 1. We had previously implemented this on the windows
platform node delegate, but for consistency's sake, and because the
default implementation is surprising, we're promoting this to the
FlutterPlatformNodeDelegate base class.

Issue: flutter/flutter#77838

TestAccessibilityBridgeDelegate::accessibility_events previously held
values of type ui::AXEventGenerator::TargetedEvent. TargetedEvent
contains an AXNode pointer and a const reference to a
ui::AXEventGenerator::EventParams object, and as such it's unsafe to
make or read copies of TargetedEvent values outside the scope of the
AccessibilityBridgeDelegate::OnAccessibilityEvent callback.

In this patch, we update the accessibility_events vector to simply hold
EventType values since this is the only part of the value we use in our
existing tests. If in future we need the full TargetedEvent, we'll need
to properly copy these values.

This patch also fixes a typo in the accessibility_events identifier and
converts an EXPECT_EQ to an ASSERT_EQ in a case where the following
test expectations are meaningless/could crash if the
accessibility_events size isn't as expected.

Issue: flutter/flutter#77838

This enables unittests for the accessibility bridge in
common_cpp_unittests, when running on Windows. Previously, we only
tested on macOS.

Issue: flutter/flutter#77838

This enables unittests for the accessibility bridge in
common_cpp_unittests, when running on Windows. Previously, we only
tested on macOS.

Issue: flutter/flutter#77838

The default implementation of GetUniqueId on ui::AXPlatformNodeDelegate
always returns ID 1. We had previously implemented this on the windows
platform node delegate, but for consistency's sake, and because the
default implementation is surprising, we're promoting this to the
FlutterPlatformNodeDelegate base class.

Issue: flutter/flutter#77838

This adds support for toggle switches such as the material Switch and
CupertinoSwitch widgets. Previously, we added support for checkboxes on
desktop platforms, but not for toggle switches.

Issue: flutter/flutter#77838

Adds support to the common desktop accessibility bridge for widgets that
include a semantics node with the `isSlider` flag set.

Issue: flutter/flutter#77838

Adds support to the common desktop accessibility bridge for widgets that
include a semantics node with the `isSlider` flag set.

Issue: flutter/flutter#77838

Microsoft Active Accessibility (MSAA) does not include
increment/decrement keyboard shortcuts for manipulating sliders and
other similar controls. To make up for this, we give the slider keyboard
focus when it gains accessibility focus so that the user can use the
arrow keys to manipulate the slider.

Issue: flutter#77838

Microsoft Active Accessibility (MSAA) does not include
increment/decrement keyboard shortcuts for manipulating sliders and
other similar controls. To make up for this, we give the slider keyboard
focus when it gains accessibility focus so that the user can use the
arrow keys to manipulate the slider.

Issue: #77838

IAccessible objects should implement accHitTest. Our implementation, in
AXPlatformNodeWin, delegates hit testing to
AXPlatformNodeDelegate::HitTestSync. Here, we do a quick recursive
depth-first walk of the accessibility tree to return the best match.

We define the best match as the deepest node in the tree that contains
the point under test whose children do not.

This also adds a ToScreenPoint() method to FlutterWindowWin32 which
avoids a raw Win32 API call, which facilitates mocking out the behaviour
of this method in tests. Since we don't have a valid HWND in unittests,
ClientToScreen() always returns the point 0,0.

Issue: flutter/flutter#77838

IAccessible objects should implement accHitTest. Our implementation, in
AXPlatformNodeWin, delegates hit testing to
AXPlatformNodeDelegate::HitTestSync. Here, we do a quick recursive
depth-first walk of the accessibility tree to return the best match.

We define the best match as the deepest node in the tree that contains
the point under test whose children do not.

Issue: flutter/flutter#77838

IAccessible objects should implement accHitTest. Our implementation, in
AXPlatformNodeWin, delegates hit testing to
AXPlatformNodeDelegate::HitTestSync. Here, we do a quick recursive
depth-first walk of the accessibility tree to return the best match.

We define the best match as the deepest node in the tree that contains
the point under test whose children do not.

Issue: flutter/flutter#77838

IAccessible objects should implement accHitTest. Our implementation, in
AXPlatformNodeWin, delegates hit testing to
AXPlatformNodeDelegate::HitTestSync. Here, we do a quick recursive
depth-first walk of the accessibility tree to return the best match.

We define the best match as the deepest node in the tree that contains
the point under test whose children do not.

Issue: flutter/flutter#77838