Keeping track of descendants that draw content instead of recalcualting

cc/layers/heads_up_display_layer.cc

 // Copyright 2012 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/layers/heads_up_display_layer.h"
 
 #include <algorithm>
 
 #include "base/debug/trace_event.h"
 #include "cc/layers/heads_up_display_layer_impl.h"
 #include "cc/trees/layer_tree_host.h"
 
 namespace cc {
 
 scoped_refptr<HeadsUpDisplayLayer> HeadsUpDisplayLayer::Create() {
   return make_scoped_refptr(new HeadsUpDisplayLayer());
 }
 
-HeadsUpDisplayLayer::HeadsUpDisplayLayer() {}
+HeadsUpDisplayLayer::HeadsUpDisplayLayer() {
+  SetIsDrawable(true);
+  UpdateDrawsContent(HasDrawableContent());
+}
 
 HeadsUpDisplayLayer::~HeadsUpDisplayLayer() {}
 
 void HeadsUpDisplayLayer::PrepareForCalculateDrawProperties(
     const gfx::Size& device_viewport, float device_scale_factor) {
   gfx::Size device_viewport_in_layout_pixels = gfx::Size(
       device_viewport.width() / device_scale_factor,
       device_viewport.height() / device_scale_factor);
 
   gfx::Size bounds;
@@ skipping 10 matching lines @@
   } else {
     int size = 256;
     bounds.SetSize(size, size);
     matrix.Translate(device_viewport_in_layout_pixels.width() - size, 0.0);
   }
 
   SetBounds(bounds);
   SetTransform(matrix);
 }
 
-bool HeadsUpDisplayLayer::DrawsContent() const { return true; }
+bool HeadsUpDisplayLayer::HasDrawableContent() const {
+  return true;
+}
 
 scoped_ptr<LayerImpl> HeadsUpDisplayLayer::CreateLayerImpl(
     LayerTreeImpl* tree_impl) {
   return HeadsUpDisplayLayerImpl::Create(tree_impl, layer_id_).
       PassAs<LayerImpl>();
 }
 
 }  // namespace cc