[Android] Support double-tap selection

ui/events/gesture_detection/gesture_detector.h

Index: ui/events/gesture_detection/gesture_detector.h
diff --git a/ui/events/gesture_detection/gesture_detector.h b/ui/events/gesture_detection/gesture_detector.h
index 07e90e138e48d5bf2863ff61748b51da2f1aaa5d..6fbbd0f5e5cb946fcb1b5c03ecabf774f89b374e 100644
--- a/ui/events/gesture_detection/gesture_detector.h
+++ b/ui/events/gesture_detection/gesture_detector.h
@@ -69,6 +69,11 @@ class GESTURE_DETECTION_EXPORT GestureDetector {
     // Maximum time the second pointer can be active for a two finger tap.
     base::TimeDelta two_finger_tap_timeout;
 
+    // Single tap count repetition length. Defaults to 1 (no repetition count).
+    // Note that when double-tap detection is enabled, the single tap repeat
+    // count will always be 1.
+    int single_tap_repeat_length;
+
     VelocityTracker::Strategy velocity_tracker_strategy;
   };
 
@@ -134,6 +139,9 @@ class GESTURE_DETECTION_EXPORT GestureDetector {
   // up events). Can only be true if there is a double tap listener attached.
   bool is_double_tapping_;
 
+  int single_tap_count_;

[tdresser, 2015/09/23 14:10:46]

The semantics of this variable feel a bit confusing.
Would it be clearer if this was the number of taps that have already happened
during the current tap sequence, instead of the tap count of the next tap to
occur?

[jdduke (slow), 2015/09/23 19:56:04]

Yeah, though I think we'll need an auxiliary variable to indicate that the
current touch sequence is possibly a repeated one (the IsConsideredDoubleTap
check needs to happen on DOWN for several reasons).

[tdresser, 2015/09/24 12:05:00]

Thanks - I find this easier to follow.

+  int single_tap_repeat_length_;
+
   float last_focus_x_;
   float last_focus_y_;
   float down_focus_x_;