Fire accessibilityPrivate events on two-finger hold gesture.

ash/accessibility_delegate.h

Index: ash/accessibility_delegate.h
diff --git a/ash/accessibility_delegate.h b/ash/accessibility_delegate.h
index ce2674b27aefe22a7adc4261c21f9a975e9e3d19..0be79b5514ed25b66e5c0768a76b47c6c56e22ad 100644
--- a/ash/accessibility_delegate.h
+++ b/ash/accessibility_delegate.h
@@ -133,6 +133,14 @@ class ASH_EXPORT AccessibilityDelegate {
   // Gets the last accessibility alert that was triggered.
   virtual AccessibilityAlert GetLastAccessibilityAlert() = 0;
 
+  // Called when we first detect two fingers are held down, which can be
+  // used to toggle spoken feedback on some touch-only devices.
+  virtual void OnTwoFingerTouchStart() {}
+
+  // Called when the user is no longer holding down two fingers (including
+  // releasing one, holding down three, or moving them).
+  virtual void OnTwoFingerTouchStop() {}
+
   // Whether or not to enable toggling spoken feedback via holding down
   // two fingers on the screen.
   virtual bool ShouldToggleSpokenFeedbackViaTouch() = 0;