Use Blink's flag to prevent fling boosting.

content/renderer/input/input_handler_proxy.cc

Index: content/renderer/input/input_handler_proxy.cc
diff --git a/content/renderer/input/input_handler_proxy.cc b/content/renderer/input/input_handler_proxy.cc
index 0d4b17320a1986903d7c6942d404731474f9c534..365722c3904b1048e03ec730bae4fe4c9e3cbf70 100644
--- a/content/renderer/input/input_handler_proxy.cc
+++ b/content/renderer/input/input_handler_proxy.cc
@@ -535,6 +535,9 @@ bool InputHandlerProxy::FilterInputEventForFlingBoosting(
   const WebGestureEvent& gesture_event =
       static_cast<const WebGestureEvent&>(event);
   if (gesture_event.type == WebInputEvent::GestureFlingCancel) {
+    if (gesture_event.data.flingCancel.preventBoosting)

[jdduke (slow), 2014/12/10 19:02:52]

Awesome, could you add a short test in input_handler_proxy_unittest.cc? There
are a number of existing tests of the form |NoFlingBoostIf*| there already, you
can basically just copy one of those and update the preventBoosting bit and make
sure it does the right thing. The |NoFlingBoostIfFlingTooSlow| code is probably
most similar to how you want to structure the test.

+      return false;
+
     if (current_fling_velocity_.LengthSquared() < kMinBoostFlingSpeedSquare)
       return false;