Avoid an extra GestureDetector instance for double-tap drag zooming

ui/events/gesture_detection/gesture_config_helper_android.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/gesture_config_helper.h"
 
 #include "ui/gfx/android/view_configuration.h"
 #include "ui/gfx/screen.h"
 
 using gfx::ViewConfiguration;
@@ skipping 31 matching lines @@
   config.maximum_fling_velocity =
       ViewConfiguration::GetMaximumFlingVelocityInPixelsPerSecond() * px_to_dp;
 
   return config;
 }
 
 ScaleGestureDetector::Config DefaultScaleGestureDetectorConfig(
     const gfx::Display& display) {
   ScaleGestureDetector::Config config;
 
-  config.gesture_detector_config = DefaultGestureDetectorConfig(display);
-  config.quick_scale_enabled = true;
-
   const float px_to_dp = 1.f / display.device_scale_factor();
+  config.span_slop = ViewConfiguration::GetTouchSlopInPixels() * 2.f * px_to_dp;
   config.min_scaling_touch_major =
       ViewConfiguration::GetMinScalingTouchMajorInPixels() * px_to_dp;
   config.min_scaling_span =
       ViewConfiguration::GetMinScalingSpanInPixels() * px_to_dp;
+  config.min_pinch_update_span_delta = 0.f;
 
   return config;
 }
 
 }  // namespace
 
 GestureProvider::Config DefaultGestureProviderConfig() {
   GestureProvider::Config config;
   config.display = gfx::Screen::GetNativeScreen()->GetPrimaryDisplay();
   config.gesture_detector_config = DefaultGestureDetectorConfig(config.display);
   config.scale_gesture_detector_config =
       DefaultScaleGestureDetectorConfig(config.display);
   config.gesture_begin_end_types_enabled = false;
   config.min_gesture_bounds_length = kMinGestureBoundsLengthDips;
   config.max_gesture_bounds_length = kMaxGestureBoundsLengthDips;
   return config;
 }
 
 }  // namespace ui