A11y: UIA: Read deleted characters in <input>

On the Windows+UIA platform, Narrator was not announcing recently
deleted characters in an <input type="text"> field when 'backspacing'
over them.

Comparing the UIA implementation in Chromium & EdgeHTML, we found that
we should fire a TextChanged event in addition to the ValueChanged event
in this scenario.

Bug: 1034729
Change-Id: Ib7423bd22cd709ac4813cfb3c0813911c704430e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1970765Reviewed-by: Kurt Catti-Schmidt <kschmi@microsoft.com>
Commit-Queue: Ian Prest <iapres@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#725609}

content/browser/accessibility/browser_accessibility_manager_win.cc

@@ -383,6 +383,7 @@ void BrowserAccessibilityManagerWin::FireGeneratedEvent(
         aria_properties_events_.insert(node);
       } else if (ui::IsValuePatternSupported(node)) {
         FireUiaPropertyChangedEvent(UIA_ValueValuePropertyId, node);
+        FireUiaTextContainerEvent(UIA_Text_TextChangedEventId, node);
       }
       break;
     case ui::AXEventGenerator::Event::VALUE_MAX_CHANGED:

content/test/data/accessibility/event/value-value-changed-expected-uia-win.txt

+Text_TextChanged on role=textbox
 ValueValue changed on role=textbox
 === Start Continuation ===
+Text_TextChanged on role=textbox
 ValueValue changed on role=textbox