Add multi-finger swipe detection to GestureDetector

ui/events/gesture_detection/gesture_config_helper_aura.cc

Index: ui/events/gesture_detection/gesture_config_helper_aura.cc
diff --git a/ui/events/gesture_detection/gesture_config_helper_aura.cc b/ui/events/gesture_detection/gesture_config_helper_aura.cc
index e7845ac621e5a53121b34d157a5be1b06956f809..f9824dde5a0dd284b0642850ddb221ae9477f267 100644
--- a/ui/events/gesture_detection/gesture_config_helper_aura.cc
+++ b/ui/events/gesture_detection/gesture_config_helper_aura.cc
@@ -27,6 +27,10 @@ GestureDetector::Config DefaultGestureDetectorConfig() {
       GestureConfiguration::min_scroll_velocity();
   config.maximum_fling_velocity =
       GestureConfiguration::fling_velocity_cap();
+  config.swipe_enabled = true;
+  config.minimum_swipe_velocity = GestureConfiguration::min_swipe_speed();
+  config.minimum_swipe_direction_ratio =

[tdresser, 2014/04/22 15:27:16]

This name isn't great, nor was the previous one.

We could rename it minimum_swipe_deviation_angle, and do a wee bit of trig?

Side note: we're caching these configuration values all over the place, which
will make getting about://gesture up and running with the unified GR a bit of a
pain. I'm not sure how we'll want to approach that.

[jdduke (slow), 2014/04/24 00:54:29]

Yeah that's better, though I'll probably cache the cotan(angle) value to get the
ratio when initializing the GestureDetector.

+      GestureConfiguration::max_swipe_deviation_ratio();
 
   return config;
 }