Avoid an extra GestureDetector instance for double-tap drag zooming

ui/events/gesture_detection/gesture_config_helper_aura.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 <cmath>
 
 #include "base/command_line.h"
 #include "ui/events/event_switches.h"
@@ skipping 34 matching lines @@
 }
 
 ScaleGestureDetector::Config DefaultScaleGestureDetectorConfig() {
   ScaleGestureDetector::Config config;
   double min_pinch_update_distance =
       CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kCompensateForUnstablePinchZoom)
           ? GestureConfiguration::min_pinch_update_distance_in_pixels()
           : 0;
 
-  config.gesture_detector_config = DefaultGestureDetectorConfig();
+  config.span_slop =
+      GestureConfiguration::max_touch_move_in_pixels_for_click() * 2;
   config.min_scaling_touch_major = GestureConfiguration::default_radius() * 2;
   config.min_scaling_span = GestureConfiguration::min_scaling_span_in_pixels();
   config.min_pinch_update_span_delta = min_pinch_update_distance;
   return config;
 }
 
 }  // namespace
 
 GestureProvider::Config DefaultGestureProviderConfig() {
   GestureProvider::Config config;
   gfx::Screen* screen = gfx::Screen::GetScreenByType(gfx::SCREEN_TYPE_NATIVE);
   // |screen| is sometimes NULL during tests.
   if (screen)
     config.display = screen->GetPrimaryDisplay();
   config.gesture_detector_config = DefaultGestureDetectorConfig();
   config.scale_gesture_detector_config = DefaultScaleGestureDetectorConfig();
   config.gesture_begin_end_types_enabled = true;
   // Half the size of the default touch length is a reasonable minimum.
   config.min_gesture_bounds_length = GestureConfiguration::default_radius();
   return config;
 }
 
 }  // namespace ui