Adopt ui::GestureConfiguration on Android

ui/events/gesture_detection/gesture_configuration_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_configuration.h"
+
+#include <cmath>
+
+#include "ui/gfx/screen.h"
+
+namespace ui {
+
+class GESTURE_DETECTION_EXPORT GestureConfigurationAura
+    : public GestureConfiguration {
+ public:
+  static GestureConfigurationAura* GetInstance() {
+    return Singleton<GestureConfigurationAura>::get();
+  }
+
+  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 = default_radius();
+    return config;
+  }
+
+  virtual GestureDetector::Config DefaultGestureDetectorConfig() override {
+    GestureDetector::Config config =
+        GestureConfiguration::DefaultGestureDetectorConfig();
+    config.swipe_enabled = true;

[jdduke (slow), 2014/10/22 00:45:12]

If we add |swipe_enabled|, |two_finger_tap_enabled| and
|gesture_begin_end_types_enabled| as members of GestureConfiguration, can we
then have just a single implementation of DefaultGestureProviderConfig(), 
DefaultGestureDetectorConfig() and  DefaultScaleGestureDetectorConfig()? I think
one of the primary motivations in this patch was allowing
GestureProvider::Config creation directly from a GestureConfiguration instance.

+    config.minimum_swipe_velocity = min_swipe_speed();
+    config.maximum_swipe_deviation_angle = max_swipe_deviation_angle();
+    config.two_finger_tap_enabled = true;
+    config.two_finger_tap_max_separation =
+        max_distance_for_two_finger_tap_in_pixels();
+    config.two_finger_tap_timeout = base::TimeDelta::FromMilliseconds(
+        max_touch_down_duration_for_click_in_ms());
+    return config;
+  }
+
+ private:
+  GestureConfigurationAura() : GestureConfiguration() {
+    set_span_slop(max_touch_move_in_pixels_for_click() * 2);
+    set_min_scaling_touch_major(default_radius() * 2);
+    set_min_pinch_update_span_delta(
+        CommandLine::ForCurrentProcess()->HasSwitch(
+            switches::kCompensateForUnstablePinchZoom)
+            ? min_pinch_update_distance_in_pixels()
+            : 0);
+  }
+  friend struct DefaultSingletonTraits<GestureConfigurationAura>;
+  DISALLOW_COPY_AND_ASSIGN(GestureConfigurationAura);
+};
+
+GestureConfiguration* GestureConfiguration::GetInstance() {
+  return GestureConfigurationAura::GetInstance();
+}
+
+GestureProvider::Config DefaultGestureProviderConfig() {
+  return GestureConfigurationAura::GetInstance()
+      ->DefaultGestureProviderConfig();
+}
+
+}  // namespace ui