Let the browser know the end of fling

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/debug/trace_event.h"
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "content/renderer/input/input_handler_proxy_client.h"
@@ skipping 277 matching lines @@
       }
       fling_parameters_.delta =
           WebFloatPoint(gesture_event.data.flingStart.velocityX,
                         gesture_event.data.flingStart.velocityY);
       fling_parameters_.point = WebPoint(gesture_event.x, gesture_event.y);
       fling_parameters_.globalPoint =
           WebPoint(gesture_event.globalX, gesture_event.globalY);
       fling_parameters_.modifiers = gesture_event.modifiers;
       fling_parameters_.sourceDevice = gesture_event.sourceDevice;
       input_handler_->ScheduleAnimation();
+      client_->DidStartFlinging();
       return DID_HANDLE;
     }
     case cc::InputHandler::ScrollOnMainThread: {
       TRACE_EVENT_INSTANT0("renderer",
                            "InputHandlerProxy::HandleGestureFling::"
                            "scroll_on_main_thread",
                            TRACE_EVENT_SCOPE_THREAD);
       fling_may_be_active_on_main_thread_ = true;
+      client_->DidStartFlinging();

[jdduke (slow), 2014/01/10 17:45:59]

So, if the fling goes unhandled by main, the |DidStart()| will be terminated by
the NOT_CONSUMED ack? 

       return DID_NOT_HANDLE;
     }
     case cc::InputHandler::ScrollIgnored: {
       TRACE_EVENT_INSTANT0(
           "renderer",
           "InputHandlerProxy::HandleGestureFling::ignored",
           TRACE_EVENT_SCOPE_THREAD);
       if (gesture_event.sourceDevice == WebGestureEvent::Touchpad) {
         // We still pass the curve to the main thread if there's nothing
         // scrollable, in case something
@@ skipping 29 matching lines @@
   } else {
     TRACE_EVENT_INSTANT0("renderer",
                          "InputHandlerProxy::animate::flingOver",
                          TRACE_EVENT_SCOPE_THREAD);
     CancelCurrentFling();
   }
 }
 
 void InputHandlerProxy::MainThreadHasStoppedFlinging() {
   fling_may_be_active_on_main_thread_ = false;
+  client_->DidStopFlinging();
 }
 
 void InputHandlerProxy::DidOverscroll(const cc::DidOverscrollParams& params) {
   DCHECK(client_);
   if (fling_curve_) {
     static const int kFlingOverscrollThreshold = 1;
     disallow_horizontal_fling_scroll_ |=
         std::abs(params.accumulated_overscroll.x()) >=
         kFlingOverscrollThreshold;
     disallow_vertical_fling_scroll_ |=
@@ skipping 16 matching lines @@
   }
 
   TRACE_EVENT_INSTANT1("renderer",
                        "InputHandlerProxy::CancelCurrentFling",
                        TRACE_EVENT_SCOPE_THREAD,
                        "had_fling_animation",
                        had_fling_animation);
   fling_curve_.reset();
   gesture_scroll_on_impl_thread_ = false;
   fling_parameters_ = blink::WebActiveWheelFlingParameters();
+  if (had_fling_animation)
+    client_->DidStopFlinging();
   return had_fling_animation;
 }
 
 bool InputHandlerProxy::TouchpadFlingScroll(
     const WebFloatSize& increment) {
   WebMouseWheelEvent synthetic_wheel;
   synthetic_wheel.type = WebInputEvent::MouseWheel;
   synthetic_wheel.deltaX = increment.width;
   synthetic_wheel.deltaY = increment.height;
   synthetic_wheel.hasPreciseScrollingDeltas = true;
@@ skipping 74 matching lines @@
   TRACE_EVENT2("renderer",
                "InputHandlerProxy::notifyCurrentFlingVelocity",
                "vx",
                velocity.width,
                "vy",
                velocity.height);
   input_handler_->NotifyCurrentFlingVelocity(ToClientScrollIncrement(velocity));
 }
 
 }  // namespace content