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

ui/events/gesture_detection/scale_gesture_detector.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_EVENTS_GESTURE_DETECTION_SCALE_GESTURE_DETECTOR_H_
 #define UI_EVENTS_GESTURE_DETECTION_SCALE_GESTURE_DETECTOR_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "base/time/time.h"
 #include "ui/events/gesture_detection/gesture_detection_export.h"
@@ skipping 53 matching lines @@
   //
   // Returns true if the event was processed and the detector wants to receive
   // the rest of the MotionEvents in this event stream.
   bool OnTouchEvent(const MotionEvent& event);
 
   // Set whether the associated |ScaleGestureListener| should receive
   // OnScale callbacks when the user performs a doubletap followed by a swipe.
   void SetQuickScaleEnabled(bool scales);
   bool IsQuickScaleEnabled() const;
   bool IsInProgress() const;
+  bool InDoubleTapMode() const;
   float GetFocusX() const;
   float GetFocusY() const;
   float GetCurrentSpan() const;
   float GetCurrentSpanX() const;
   float GetCurrentSpanY() const;
   float GetPreviousSpan() const;
   float GetPreviousSpanX() const;
   float GetPreviousSpanY() const;
   float GetScaleFactor() const;
   base::TimeDelta GetTimeDelta() const;
   base::TimeTicks GetEventTime() const;
 
  private:
   enum DoubleTapMode { DOUBLE_TAP_MODE_NONE, DOUBLE_TAP_MODE_IN_PROGRESS };
 
   // DoubleTapListener implementation.
   virtual bool OnDoubleTap(const MotionEvent& ev) OVERRIDE;
 
   // The TouchMajor/TouchMinor elements of a MotionEvent can flutter/jitter on
   // some hardware/driver combos. Smooth out to get kinder, gentler behavior.
   void AddTouchHistory(const MotionEvent& ev);
   void ClearTouchHistory();
-  bool InDoubleTapMode() const;
 
   ScaleGestureListener* const listener_;
 
   Config config_;
 
   float focus_x_;
   float focus_y_;
 
   bool quick_scale_enabled_;
 
@@ skipping 24 matching lines @@
   bool event_before_or_above_starting_gesture_event_;
 
   scoped_ptr<GestureDetector> gesture_detector_;
 
   DISALLOW_COPY_AND_ASSIGN(ScaleGestureDetector);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_GESTURE_DETECTION_SCALE_GESTURE_DETECTOR_H_