Fix state change narration for ImageToggleButton in save password dialog

This PR makes the ImageToggleButton class fire a kCheckedStateChanged
event on state changes instead of kAriaAttributeChanged. This fixes an
issue where NVDA was not announcing the state change.

The kCheckedStateChanged event is also handled in
AXPlatformNodeWin::MojoEventToUIAProperty. We map it to
UIA_ToggleToggleStatePropertyId, which makes Narrator announce the
state changes as well.

Tested locally:

* Narrator works with --enable-experimental-ui-automation.
* NVDA works both with and without the experimental flag.
* MacOS VoiceOver works.

Bug: 1013835
Change-Id: I925aad65925aadc34468651198bed39c2ba8776a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1861915Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Sumit Sahrawat <Sumit.Sahrawat@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#707230}

ui/accessibility/platform/ax_platform_node_win.cc

@@ -6890,6 +6890,8 @@ base::Optional<PROPERTYID> AXPlatformNodeWin::MojoEventToUIAProperty(
   switch (event) {
     case ax::mojom::Event::kControlsChanged:
       return UIA_ControllerForPropertyId;
+    case ax::mojom::Event::kCheckedStateChanged:
+      return UIA_ToggleToggleStatePropertyId;
     default:
       return base::nullopt;
   }

ui/views/controls/button/image_button.cc

@@ -228,7 +228,7 @@ void ToggleImageButton::SetToggled(bool toggled) {
   toggled_ = toggled;
   SchedulePaint();
 
-  NotifyAccessibilityEvent(ax::mojom::Event::kAriaAttributeChanged, true);
+  NotifyAccessibilityEvent(ax::mojom::Event::kCheckedStateChanged, true);
 }
 
 void ToggleImageButton::SetToggledImage(ButtonState image_state,