Fix race conditions in window snapshot code.

cc/trees/layer_tree_host.h

Index: cc/trees/layer_tree_host.h
diff --git a/cc/trees/layer_tree_host.h b/cc/trees/layer_tree_host.h
index ba91e119df1a95545d9cfd7f1a388923fc4f4ae4..2d811918bffb4e6854ee428487b7d8394c3a5dff 100644
--- a/cc/trees/layer_tree_host.h
+++ b/cc/trees/layer_tree_host.h
@@ -195,6 +195,8 @@ class CC_EXPORT LayerTreeHost : NON_EXPORTED_BASE(public RateLimiterClient) {
 
   void SetNextCommitWaitsForActivation();
 
+  void SetNextCommitForcesRedraw();
+
   void SetAnimationEvents(scoped_ptr<AnimationEventsVector> events,
                           base::Time wall_clock_time);
 
@@ -422,6 +424,7 @@ class CC_EXPORT LayerTreeHost : NON_EXPORTED_BASE(public RateLimiterClient) {
   };
   LCDTextMetrics lcd_text_metrics_;
   int tree_id_;
+  bool next_commit_forces_redraw_;
 
   scoped_refptr<Layer> page_scale_layer_;
   scoped_refptr<Layer> inner_viewport_scroll_layer_;