Avoid an extra GestureDetector instance for double-tap drag zooming

ui/events/gesture_detection/scale_gesture_detector.h

Index: ui/events/gesture_detection/scale_gesture_detector.h
diff --git a/ui/events/gesture_detection/scale_gesture_detector.h b/ui/events/gesture_detection/scale_gesture_detector.h
index 7f647c0684cceae31232928ab811f0003d7a87a5..9b1c9a8927af527ef1f43ff1f01e952369e21c4f 100644
--- a/ui/events/gesture_detection/scale_gesture_detector.h
+++ b/ui/events/gesture_detection/scale_gesture_detector.h
@@ -5,10 +5,8 @@
 #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"
-#include "ui/events/gesture_detection/gesture_detector.h"
 
 namespace ui {
 
@@ -18,12 +16,16 @@ class MotionEvent;
 // * platform/frameworks/base/core/java/android/view/ScaleGestureDetector.java
 // * Change-Id: I3e7926a4f6f9ab4951f380bd004499c78b3bda69
 // * Please update the Change-Id as upstream Android changes are pulled.
-class ScaleGestureDetector : public GestureDetector::SimpleGestureListener {
+class ScaleGestureDetector {
  public:
   struct GESTURE_DETECTION_EXPORT Config {
     Config();
     ~Config();
-    GestureDetector::Config gesture_detector_config;
+
+    // Distance the current span can deviate from the initial span before
+    // scaling will start (in dips). The span is the diameter of the circle with
+    // a radius of average pointer deviation from the focal point.
+    float span_slop;
 
     // Minimum accepted value for TouchMajor while scaling (in dips).
     float min_scaling_touch_major;
@@ -31,9 +33,6 @@ class ScaleGestureDetector : public GestureDetector::SimpleGestureListener {
     // Minimum span needed to initiate a scaling gesture (in dips).
     float min_scaling_span;
 
-    // Whether double-tap drag scaling is enabled.
-    bool quick_scale_enabled;
-
     // Minimum pinch span change before pinch occurs (in dips). See
     // crbug.com/373318.
     float min_pinch_update_span_delta;
@@ -82,10 +81,14 @@ class ScaleGestureDetector : public GestureDetector::SimpleGestureListener {
   // the rest of the MotionEvents in this event stream.
   bool OnTouchEvent(const MotionEvent& event);
 
+  // This method may be called by the owner when a a double-tap event has been
+  // detected *for the same event stream* being fed to this instance of the
+  // ScaleGestureDetector. As call order is important here, the double-tap
+  // detector should always be offered events *before* the ScaleGestureDetector.
+  bool OnDoubleTap(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;
@@ -103,9 +106,6 @@ class ScaleGestureDetector : public GestureDetector::SimpleGestureListener {
  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);
@@ -115,13 +115,8 @@ class ScaleGestureDetector : public GestureDetector::SimpleGestureListener {
 
   ScaleGestureListener* const listener_;
 
-  Config config_;
-
   float focus_x_;
   float focus_y_;
-
-  bool quick_scale_enabled_;
-
   float curr_span_;
   float prev_span_;
   float initial_span_;
@@ -149,8 +144,6 @@ class ScaleGestureDetector : public GestureDetector::SimpleGestureListener {
 
   bool event_before_or_above_starting_gesture_event_;
 
-  scoped_ptr<GestureDetector> gesture_detector_;
-
   DISALLOW_COPY_AND_ASSIGN(ScaleGestureDetector);
 };