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

ui/events/gesture_detection/scale_gesture_detector.cc

 // 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.
 
 #include "ui/events/gesture_detection/scale_gesture_detector.h"
 
 #include <limits.h>
 #include <cmath>
 
 #include "base/float_util.h"
 #include "base/logging.h"
 #include "ui/events/gesture_detection/motion_event.h"
 
 using base::TimeDelta;
 using base::TimeTicks;
 
 namespace ui {
 namespace {
 
 const int kTouchStabilizeTimeMs = 128;
 
 const float kScaleFactor = .5f;
 
 }  // namespace
 
 // Note: These constants were taken directly from the default (unscaled)
 // versions found in Android's ViewConfiguration.
 ScaleGestureDetector::Config::Config()
-    : quick_scale_enabled(false),
+    : quick_scale_enabled(true),
       min_scaling_touch_major(48),
       min_scaling_span(200) {}
 
 ScaleGestureDetector::Config::~Config() {}
 
 bool ScaleGestureDetector::SimpleScaleGestureListener::OnScale(
     const ScaleGestureDetector&) {
   return false;
 }
 
@@ skipping 198 matching lines @@
         new GestureDetector(config_.gesture_detector_config, this, this));
   }
 }
 
 bool ScaleGestureDetector::IsQuickScaleEnabled() const {
   return quick_scale_enabled_;
 }
 
 bool ScaleGestureDetector::IsInProgress() const { return in_progress_; }
 
+bool ScaleGestureDetector::InDoubleTapMode() const {
+  return double_tap_mode_ == DOUBLE_TAP_MODE_IN_PROGRESS;
+}
+
 float ScaleGestureDetector::GetFocusX() const { return focus_x_; }
 
 float ScaleGestureDetector::GetFocusY() const { return focus_y_; }
 
 float ScaleGestureDetector::GetCurrentSpan() const { return curr_span_; }
 
 float ScaleGestureDetector::GetCurrentSpanX() const { return curr_span_x_; }
 
 float ScaleGestureDetector::GetCurrentSpanY() const { return curr_span_y_; }
 
@@ skipping 95 matching lines @@
 }
 
 void ScaleGestureDetector::ClearTouchHistory() {
   touch_upper_ = std::numeric_limits<float>::quiet_NaN();
   touch_lower_ = std::numeric_limits<float>::quiet_NaN();
   touch_history_last_accepted_ = std::numeric_limits<float>::quiet_NaN();
   touch_history_direction_ = 0;
   touch_history_last_accepted_time_ = base::TimeTicks();
 }
 
-bool ScaleGestureDetector::InDoubleTapMode() const {
-  return double_tap_mode_ == DOUBLE_TAP_MODE_IN_PROGRESS;
-}
-
 }  // namespace ui