Keeping track of descendants that draw content instead of recalcualting

cc/layers/picture_image_layer.cc

Index: cc/layers/picture_image_layer.cc
diff --git a/cc/layers/picture_image_layer.cc b/cc/layers/picture_image_layer.cc
index a65ac8c9318c498a22ca904a00edc1ab5a7994ee..4c673e804a3679e6af84b0728097443b86ce66bc 100644
--- a/cc/layers/picture_image_layer.cc
+++ b/cc/layers/picture_image_layer.cc
@@ -24,8 +24,8 @@ scoped_ptr<LayerImpl> PictureImageLayer::CreateLayerImpl(
   return PictureImageLayerImpl::Create(tree_impl, id()).PassAs<LayerImpl>();
 }
 
-bool PictureImageLayer::DrawsContent() const {
-  return !bitmap_.isNull() && PictureLayer::DrawsContent();
+void PictureImageLayer::UpdateDrawsContent(bool draws_content) {
+  return PictureLayer::UpdateDrawsContent(draws_content && !bitmap_.isNull());
 }
 
 void PictureImageLayer::SetBitmap(const SkBitmap& bitmap) {
@@ -37,6 +37,7 @@ void PictureImageLayer::SetBitmap(const SkBitmap& bitmap) {
     return;
 
   bitmap_ = bitmap;
+  UpdateDrawsContent(true);
   SetNeedsDisplay();
 }