Use floor time to limit requestAnimationFrame in compositing mode if there are no swaps pending

content/renderer/render_widget.cc

 // Copyright (c) 2012 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/render_widget.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
@@ skipping 706 matching lines @@
 
 void RenderWidget::AnimateIfNeeded() {
   if (!animation_update_pending_)
     return;
 
   // Target 60FPS if vsync is on. Go as fast as we can if vsync is off.
   base::TimeDelta animationInterval = IsRenderingVSynced() ?
       base::TimeDelta::FromMilliseconds(16) : base::TimeDelta();
 
   base::Time now = base::Time::Now();
-  if (now >= animation_floor_time_ || is_accelerated_compositing_active_) {
+
+  // animation_floor_time_ is the earliest time that we should animate when
+  // using the dead reckoning software scheduler. If we're using swapbuffers
+  // complete callbacks to rate limit, we can ignore this floor.
+  if (now >= animation_floor_time_ || num_swapbuffers_complete_pending_ > 0) {
     TRACE_EVENT0("renderer", "RenderWidget::AnimateIfNeeded")
     animation_floor_time_ = now + animationInterval;
     // Set a timer to call us back after animationInterval before
     // running animation callbacks so that if a callback requests another
     // we'll be sure to run it at the proper time.
     MessageLoop::current()->PostDelayedTask(
         FROM_HERE, base::Bind(&RenderWidget::AnimationCallback, this),
         animationInterval);
     animation_task_posted_ = true;
     animation_update_pending_ = false;
@@ skipping 906 matching lines @@
   }
 }
 
 bool RenderWidget::WillHandleMouseEvent(const WebKit::WebMouseEvent& event) {
   return false;
 }
 
 bool RenderWidget::WebWidgetHandlesCompositorScheduling() const {
   return false;
 }