Keeping track of descendants that draw content instead of recalcualting

cc/layers/image_layer.cc

 // Copyright 2010 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/image_layer.h"
 
 #include "base/compiler_specific.h"
 #include "cc/resources/image_layer_updater.h"
 #include "cc/resources/layer_updater.h"
 #include "cc/resources/prioritized_resource.h"
@@ skipping 12 matching lines @@
 
 void ImageLayer::SetBitmap(const SkBitmap& bitmap) {
   // SetBitmap() currently gets called whenever there is any
   // style change that affects the layer even if that change doesn't
   // affect the actual contents of the image (e.g. a CSS animation).
   // With this check in place we avoid unecessary texture uploads.
   if (bitmap.pixelRef() && bitmap.pixelRef() == bitmap_.pixelRef())
     return;
 
   bitmap_ = bitmap;
+  UpdateDrawsContent(HasDrawableContent());
   SetNeedsDisplay();
 }
 
+bool ImageLayer::HasDrawableContent() const {
+  return !bitmap_.isNull() && TiledLayer::HasDrawableContent();
+}
+
 void ImageLayer::SetTexturePriorities(const PriorityCalculator& priority_calc) {
   // Update the tile data before creating all the layer's tiles.
   UpdateTileSizeAndTilingOption();
 
   TiledLayer::SetTexturePriorities(priority_calc);
 }
 
 bool ImageLayer::Update(ResourceUpdateQueue* queue,
                         const OcclusionTracker<Layer>* occlusion) {
   CreateUpdaterIfNeeded();
@@ skipping 24 matching lines @@
                                         float maximum_animation_contents_scale,
                                         bool animating_transform_to_screen,
                                         float* contents_scale_x,
                                         float* contents_scale_y,
                                         gfx::Size* content_bounds) {
   *contents_scale_x = ImageContentsScaleX();
   *contents_scale_y = ImageContentsScaleY();
   *content_bounds = gfx::Size(bitmap_.width(), bitmap_.height());
 }
 
-bool ImageLayer::DrawsContent() const {
-  return !bitmap_.isNull() && TiledLayer::DrawsContent();
-}
-
 void ImageLayer::OnOutputSurfaceCreated() {
   SetTextureFormat(
       layer_tree_host()->GetRendererCapabilities().best_texture_format);
   TiledLayer::OnOutputSurfaceCreated();
 }
 
 float ImageLayer::ImageContentsScaleX() const {
   if (bounds().IsEmpty() || bitmap_.width() == 0)
     return 1;
   return static_cast<float>(bitmap_.width()) / bounds().width();
 }
 
 float ImageLayer::ImageContentsScaleY() const {
   if (bounds().IsEmpty() || bitmap_.height() == 0)
     return 1;
   return static_cast<float>(bitmap_.height()) / bounds().height();
 }
 
 }  // namespace cc