Toggle spoken feedback if two fingers are held down.

ash/common/accessibility_delegate.h

Index: ash/common/accessibility_delegate.h
diff --git a/ash/common/accessibility_delegate.h b/ash/common/accessibility_delegate.h
index 36ea7080e177241a45ae30b532784bf382bd105a..0ef6cdcb0c85a15e991beb29d77162d35a180901 100644
--- a/ash/common/accessibility_delegate.h
+++ b/ash/common/accessibility_delegate.h
@@ -121,6 +121,12 @@ class ASH_EXPORT AccessibilityDelegate {
   // Gets the last accessibility alert that was triggered.
   virtual AccessibilityAlert GetLastAccessibilityAlert() = 0;
 
+  // While the user holds down two fingers on a touch screen, which is the
+  // gesture to enable spoken feedback (if held down long enough), play a sound
+  // every "tick" (approximately every half-second) to warn the user something
+  // is about to happen.

[oshima, 2016/11/08 18:14:43]

You have very similar comments in three places. 
How about keeping the comment minimum here (what implementation should do)?

[dmazzoni, 2016/11/08 20:43:47]

Made it more concise in 2/3 places

+  virtual void PlaySpokenFeedbackToggleCountdown(int tick_count) = 0;
+
   // Plays an earcon. Earcons are brief and distinctive sounds that indicate
   // when their mapped event has occurred. The sound key enums can be found in
   // chromeos/audio/chromeos_sounds.h.