Fix race conditions in window snapshot code.

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index 8bbf7429cede0c3a70f248922e9063744949a8f7..6e153d1f81ad11d3431e968c6584f2cf661ad64b 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -133,7 +133,8 @@ LayerTreeHost::LayerTreeHost(LayerTreeHostClient* client,
       partial_texture_update_requests_(0),
       in_paint_layer_contents_(false),
       total_frames_used_for_lcd_text_metrics_(0),
-      tree_id_(s_next_tree_id++) {
+      tree_id_(s_next_tree_id++),
+      next_commit_forces_redraw_(false) {
   if (settings_.accelerated_animation_enabled)
     animation_registrar_ = AnimationRegistrar::Create();
   s_num_layer_tree_instances++;
@@ -323,11 +324,17 @@ void LayerTreeHost::FinishCommitOnImplThread(LayerTreeHostImpl* host_impl) {
     DCHECK(!host_impl->pending_tree());
     host_impl->CreatePendingTree();
     sync_tree = host_impl->pending_tree();
+    if (next_commit_forces_redraw_)
+      sync_tree->ForceRedrawNextActivation();
   } else {
+    if (next_commit_forces_redraw_)
+      host_impl->SetFullRootLayerDamage();
     contents_texture_manager_->ReduceMemory(host_impl->resource_provider());
     sync_tree = host_impl->active_tree();
   }
 
+  next_commit_forces_redraw_ = false;
+
   sync_tree->set_source_frame_number(source_frame_number());
 
   if (needs_full_tree_sync_)
@@ -565,6 +572,10 @@ void LayerTreeHost::SetNextCommitWaitsForActivation() {
   proxy_->SetNextCommitWaitsForActivation();
 }
 
+void LayerTreeHost::SetNextCommitForcesRedraw() {
+  next_commit_forces_redraw_ = true;
+}
+
 void LayerTreeHost::SetAnimationEvents(scoped_ptr<AnimationEventsVector> events,
                                        base::Time wall_clock_time) {
   DCHECK(proxy_->IsMainThread());