Force a commit at the end of the top controls animation

cc/trees/layer_tree_host_impl.cc

 // Copyright 2011 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 "cc/trees/layer_tree_host_impl.h"
 
 #include <algorithm>
 #include <limits>
 
 #include "base/basictypes.h"
@@ skipping 3016 matching lines @@
 void LayerTreeHostImpl::AnimateTopControls(base::TimeTicks time) {
   if (!top_controls_manager_ || !top_controls_manager_->animation())
     return;
   gfx::Vector2dF scroll = top_controls_manager_->Animate(time);
   if (active_tree_->TotalScrollOffset().y() == 0.f)
     return;
   if (!scroll.IsZero()) {
     ScrollViewportBy(gfx::ScaleVector2d(
         scroll, 1.f / active_tree_->total_page_scale_factor()));
     SetNeedsRedraw();
+    client_->SetNeedsCommitOnImplThread();
+    client_->RenewTreePriority();
   }
-  SetNeedsAnimate();
+  if (top_controls_manager_->animation())
+    SetNeedsAnimate();

[aelias_OOO_until_Jul13, 2014/08/12 20:38:09]

Now that I look at this, this SetNeedsAnimate should be before the early-return
(or the early-return should be replaced by a && condition in the if statement). 
The early return was added in https://chromiumcodereview.appspot.com/14715002
when SetNeedsAnimate didn't exist.  Indeed I see the animation sometimes snaps
when at the top of the page.  Could you also fix this while you're at it and add
a test?

[jdduke (slow), 2014/08/12 22:48:50]

Done.

 }
 
 void LayerTreeHostImpl::AnimateLayers(base::TimeTicks monotonic_time) {
   if (!settings_.accelerated_animation_enabled ||
       !needs_animate_layers() ||
       !active_tree_->root_layer())
     return;
 
   TRACE_EVENT0("cc", "LayerTreeHostImpl::AnimateLayers");
   AnimationRegistrar::AnimationControllerMap copy =
@@ skipping 320 matching lines @@
 }
 
 void LayerTreeHostImpl::UnregisterPictureLayerImpl(PictureLayerImpl* layer) {
   std::vector<PictureLayerImpl*>::iterator it =
       std::find(picture_layers_.begin(), picture_layers_.end(), layer);
   DCHECK(it != picture_layers_.end());
   picture_layers_.erase(it);
 }
 
 }  // namespace cc