Tweaks to top controls behavior for fullscreen API support.

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 "base/basictypes.h"
 #include "base/debug/trace_event.h"
@@ skipping 1846 matching lines @@
     client_->SetNeedsCommitOnImplThread();
     client_->RenewTreePriority();
   }
 }
 
 void LayerTreeHostImpl::AnimateTopControls(base::TimeTicks time) {
   if (!top_controls_manager_ || !RootScrollLayer())
     return;
   gfx::Vector2dF scroll = top_controls_manager_->Animate(time);
   UpdateMaxScrollOffset();
+  if (RootScrollLayer()->TotalScrollOffset().y() == 0.f)
+    return;
   RootScrollLayer()->ScrollBy(gfx::ScaleVector2d(
       scroll, 1.f / active_tree_->total_page_scale_factor()));
 }
 
 void LayerTreeHostImpl::AnimateLayers(base::TimeTicks monotonic_time,
                                       base::Time wall_clock_time) {
   if (!settings_.accelerated_animation_enabled ||
       animation_registrar_->active_animation_controllers().empty() ||
       !active_tree_->root_layer())
     return;
@@ skipping 254 matching lines @@
 }
 
 void LayerTreeHostImpl::SetDebugState(const LayerTreeDebugState& debug_state) {
   if (debug_state_.continuous_painting != debug_state.continuous_painting)
     paint_time_counter_->ClearHistory();
 
   debug_state_ = debug_state;
 }
 
 }  // namespace cc