Use Blink's flag to prevent fling boosting.

content/renderer/input/input_handler_proxy.cc

 // Copyright 2013 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 "content/renderer/input/input_handler_proxy.h"
 
 #include "base/auto_reset.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
@@ skipping 517 matching lines @@
     return false;
 
   if (!fling_curve_) {
     DCHECK(!deferred_fling_cancel_time_seconds_);
     return false;
   }
 
   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;
 
     TRACE_EVENT_INSTANT0("input",
                          "InputHandlerProxy::FlingBoostStart",
                          TRACE_EVENT_SCOPE_THREAD);
     deferred_fling_cancel_time_seconds_ =
         event.timeStampSeconds + kFlingBoostTimeoutDelaySeconds;
     return true;
   }
@@ skipping 338 matching lines @@
   // trigger a scroll, e.g., with a trivial time delta between fling updates.
   // Return true in this case to prevent early fling termination.
   if (std::abs(clipped_increment.width) < kScrollEpsilon &&
       std::abs(clipped_increment.height) < kScrollEpsilon)
     return true;
 
   return did_scroll;
 }
 
 }  // namespace content