Adopt "QuickScale" double-tap drag zoom code in the GestureProvider

ui/events/gesture_detection/gesture_provider.h

Index: ui/events/gesture_detection/gesture_provider.h
diff --git a/ui/events/gesture_detection/gesture_provider.h b/ui/events/gesture_detection/gesture_provider.h
index d8542194ccecf19864e1a337354629a2826a9816..ee3d614c07f190db6c32a67a74adb9387c43d1c7 100644
--- a/ui/events/gesture_detection/gesture_provider.h
+++ b/ui/events/gesture_detection/gesture_provider.h
@@ -66,9 +66,13 @@ class GESTURE_DETECTION_EXPORT GestureProvider {
   // forwarded and detection is still active).
   bool IsPinchInProgress() const;
 
-  // Whether a double tap-gesture is in-progress.
+  // Whether a double-tap gesture is in-progress (either double-tap or
+  // double-tap drag zoom).
   bool IsDoubleTapInProgress() const;
 
+  // Whether double-tap gesture detection is supported.
+  bool IsDoubleTapSupportedEnabled() const;

[tdresser, 2014/04/03 17:53:30]

SupportedEnabled -> Supported|Enabled.

[jdduke (slow), 2014/04/03 19:28:01]

Done.

+
   // Whether the tap gesture delay is explicitly disabled (independent of
   // whether double-tap is supported), see |Config.disable_click_delay|.
   bool IsClickDelayDisabled() const;
@@ -93,6 +97,7 @@ class GESTURE_DETECTION_EXPORT GestureProvider {
   bool SendLongTapIfNecessary(const MotionEvent& event);
   void EndTouchScrollIfNecessary(base::TimeTicks time,
                                  bool send_scroll_end_event);
+  void UpdateDoubleTapDetectionSupport();
 
   GestureProviderClient* const client_;
 
@@ -120,6 +125,10 @@ class GESTURE_DETECTION_EXPORT GestureProvider {
   bool touch_scroll_in_progress_;
   bool pinch_in_progress_;
 
+  // Whether double-tap gesture detection is currently supported.
+  bool double_tap_support_for_page_;
+  bool double_tap_support_for_platform_;
+
   // Keeps track of the current GESTURE_LONG_PRESS event. If a context menu is
   // opened after a GESTURE_LONG_PRESS, this is used to insert a
   // GESTURE_TAP_CANCEL for removing any ::active styling.