arc-a11y: Use aria attribute changed event on android test change

This is a follow up of CL:2462883.
Android VIEW_TEXT_CHANGED event is value changed or name changed events
in Chrome, and both are handled by AXEventGenerator. Dispatching text
changed event is unnecessary, and actually no 1st party accessibility
extensions are lisntening this event type.

AX-Relnotes: n/a
Bug: None
Test: tast arc.AccessiblityEvent with CL:2467224.
Change-Id: Idcaf2f71c233d4890beee0d6d0fc7584f9fe1ef9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2463001Reviewed-by: David Tseng <dtseng@chromium.org>
Commit-Queue: Hiroki Sato <hirokisato@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816827}

chrome/browser/chromeos/arc/accessibility/arc_accessibility_util.cc

@@ -40,7 +40,7 @@ ax::mojom::Event ToAXEvent(
     case mojom::AccessibilityEventType::VIEW_LONG_CLICKED:
       return ax::mojom::Event::kClicked;
     case mojom::AccessibilityEventType::VIEW_TEXT_CHANGED:
-      return ax::mojom::Event::kTextChanged;
+      return ax::mojom::Event::kAriaAttributeChanged;
     case mojom::AccessibilityEventType::VIEW_TEXT_SELECTION_CHANGED:
       return ax::mojom::Event::kTextSelectionChanged;
     case mojom::AccessibilityEventType::WINDOW_STATE_CHANGED: {