Provide max gesture bounds and option to ignore touch size during pinch

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;
 
 namespace ui {
 namespace {
 // TODO(jdduke): Adopt GestureConfiguration on Android, crbug/339203.
 
 // This was the minimum tap/press size used on Android before the new gesture
 // detection pipeline.
 const float kMinGestureBoundsLengthDips = 24.f;
 
+// This value is somewhat arbitrary, but provides a reasonable maximum
+// approximating a large thumb depression.
+const float kMaxGestureBoundsLengthDips = kMinGestureBoundsLengthDips * 4.f;
+
 GestureDetector::Config DefaultGestureDetectorConfig(
     const gfx::Display& display) {
   GestureDetector::Config config;
 
   config.longpress_timeout = base::TimeDelta::FromMilliseconds(
       ViewConfiguration::GetLongPressTimeoutInMs());
   config.showpress_timeout =
       base::TimeDelta::FromMilliseconds(ViewConfiguration::GetTapTimeoutInMs());
   config.double_tap_timeout = base::TimeDelta::FromMilliseconds(
       ViewConfiguration::GetDoubleTapTimeoutInMs());
@@ skipping 14 matching lines @@
 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.min_scaling_touch_major =
       ViewConfiguration::GetMinScalingTouchMajorInPixels() * px_to_dp;
+  config.use_touch_major_in_span =
+      ViewConfiguration::ShouldUseTouchMajorInScalingSpan();
   config.min_scaling_span =
       ViewConfiguration::GetMinScalingSpanInPixels() * px_to_dp;
+  // As the |min_scaling_span| platform constant assumes that touch major values
+  // are used when computing the span, subtract off a reasonable touch major
+  // value for the case where the touch major values are not used.
+  if (!config.use_touch_major_in_span) {
+    config.min_scaling_span = std::max(
+        0.f, config.min_scaling_span - 2.f * config.min_scaling_touch_major);
+  }
 
   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