Keeping track of descendants that draw content instead of recalcualting

cc/layers/picture_layer.cc

Index: cc/layers/picture_layer.cc
diff --git a/cc/layers/picture_layer.cc b/cc/layers/picture_layer.cc
index b9f265a02a4b15d29cb7ba7f85e18e56f0454b31..d2e29b691837a39f0842fa2ddcb3d0c9808c02f0 100644
--- a/cc/layers/picture_layer.cc
+++ b/cc/layers/picture_layer.cc
@@ -28,10 +28,6 @@ PictureLayer::PictureLayer(ContentLayerClient* client)
 PictureLayer::~PictureLayer() {
 }
 
-bool PictureLayer::DrawsContent() const {
-  return Layer::DrawsContent() && client_;
-}
-
 scoped_ptr<LayerImpl> PictureLayer::CreateLayerImpl(LayerTreeImpl* tree_impl) {
   return PictureLayerImpl::Create(tree_impl, id()).PassAs<LayerImpl>();
 }
@@ -200,6 +196,15 @@ bool PictureLayer::IsSuitableForGpuRasterization() const {
   return pile_->is_suitable_for_gpu_rasterization();
 }
 
+void PictureLayer::ClearClient() {
+  client_ = NULL;
+  UpdateDrawsContent(HasDrawableContent());
+}
+
+bool PictureLayer::HasDrawableContent() const {
+  return client_ && Layer::HasDrawableContent();
+}
+
 void PictureLayer::RunMicroBenchmark(MicroBenchmark* benchmark) {
   benchmark->RunOnLayer(this);
 }