Make the fling acceleration constant adjustable from chrome://gesture

The GestureRecognizer applies an acceleration to touchscreen fling velocities
to make them align more nicely with the touchpad fling deacceleration curves.
Make this configurable from the interactive configurator.

BUG=141648


Review URL: https://chromiumcodereview.appspot.com/10861033

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@153097 0039d316-1c4b-4281-b951-d872f2087c98

4 files changed, 15 insertions, 1 deletions

diff --git a/ui/aura/test/aura_test_base.cc b/ui/aura/test/aura_test_base.cc
index e9609ee..5dbb9fc 100644
--- a/ui/aura/test/aura_test_base.cc
+++ b/ui/aura/test/aura_test_base.cc
@@ -44,6 +44,8 @@ void AuraTestBase::SetUp() {
   ui::GestureConfiguration::set_rail_break_proportion(15);
   ui::GestureConfiguration::set_rail_start_proportion(2);
   ui::GestureConfiguration::set_default_radius(0);
+  ui::GestureConfiguration::set_touchscreen_fling_acceleration_adjustment(
+      1.f / 900.f);
   helper_.reset(new AuraTestHelper(&message_loop_));
   helper_->SetUp();
 }
diff --git a/ui/base/gestures/gesture_configuration.cc b/ui/base/gestures/gesture_configuration.cc
index 5ba5f34..a53685e 100644
--- a/ui/base/gestures/gesture_configuration.cc
+++ b/ui/base/gestures/gesture_configuration.cc
@@ -36,4 +36,8 @@ int GestureConfiguration::points_buffered_for_velocity_ = 3;
 double GestureConfiguration::rail_break_proportion_ = 15;
 double GestureConfiguration::rail_start_proportion_ = 2;
 
+// The additional acceleration to apply to touchscreen flings.
+double GestureConfiguration::touchscreen_fling_acceleration_adjustment_
+    = 1.f / 900.f;
+
 }  // namespace ui
diff --git a/ui/base/gestures/gesture_configuration.h b/ui/base/gestures/gesture_configuration.h
index 1b0caa4..7deac42 100644
--- a/ui/base/gestures/gesture_configuration.h
+++ b/ui/base/gestures/gesture_configuration.h
@@ -133,6 +133,12 @@ class UI_EXPORT GestureConfiguration {
   static void set_rail_start_proportion(double val) {
     rail_start_proportion_ = val;
   }
+  static double touchscreen_fling_acceleration_adjustment() {
+    return touchscreen_fling_acceleration_adjustment_;
+  }
+  static void set_touchscreen_fling_acceleration_adjustment(double val) {
+    touchscreen_fling_acceleration_adjustment_ = val;
+  }
 
  private:
   // These are listed in alphabetical order ignoring underscores, to
@@ -169,6 +175,7 @@ class UI_EXPORT GestureConfiguration {
   static int points_buffered_for_velocity_;
   static double rail_break_proportion_;
   static double rail_start_proportion_;
+  static double touchscreen_fling_acceleration_adjustment_;
 
   DISALLOW_COPY_AND_ASSIGN(GestureConfiguration);
 };
diff --git a/ui/base/gestures/gesture_sequence.cc b/ui/base/gestures/gesture_sequence.cc
index 5039bc4..7760a0d 100644
--- a/ui/base/gestures/gesture_sequence.cc
+++ b/ui/base/gestures/gesture_sequence.cc
@@ -278,7 +278,8 @@ float CalibrateFlingVelocity(float velocity) {
   // touchpad scroll-events. This curve needs to be adjusted to work correctly
   // with both touchpad and touchscreen. Until then, scale quadratically.
   // http://crbug.com/120154
-  const float velocity_scaling  = 1.f / 900.f;
+  const float velocity_scaling  =
+      GestureConfiguration::touchscreen_fling_acceleration_adjustment();
   return velocity_scaling * velocity * fabsf(velocity);
 }