Force a commit at the end of the top controls animation

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 2d7a9323edf74e7bceb7eab96100f2d8996b12f6..fe993fa07058d717ef5e5784b6b2dc844d9a4363 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -3034,8 +3034,11 @@ void LayerTreeHostImpl::AnimateTopControls(base::TimeTicks time) {
     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) {