Skip clearing the canvas before painting the contents of opaque layers

cc/resources/bitmap_content_layer_updater.cc

 // Copyright 2011 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/resources/bitmap_content_layer_updater.h"
 
 #include "cc/debug/devtools_instrumentation.h"
 #include "cc/debug/rendering_stats_instrumentation.h"
 #include "cc/resources/layer_painter.h"
 #include "cc/resources/prioritized_resource.h"
@@ skipping 25 matching lines @@
   return make_scoped_refptr(
       new BitmapContentLayerUpdater(painter.Pass(),
                                     stats_instrumentation,
                                     layer_id));
 }
 
 BitmapContentLayerUpdater::BitmapContentLayerUpdater(
     scoped_ptr<LayerPainter> painter,
     RenderingStatsInstrumentation* stats_instrumentation,
     int layer_id)
-    : ContentLayerUpdater(painter.Pass(), stats_instrumentation, layer_id),
-      opaque_(false) {}
+    : ContentLayerUpdater(painter.Pass(), stats_instrumentation, layer_id) {}
 
 BitmapContentLayerUpdater::~BitmapContentLayerUpdater() {}
 
 scoped_ptr<LayerUpdater::Resource> BitmapContentLayerUpdater::CreateResource(
     PrioritizedResourceManager* manager) {
   return scoped_ptr<LayerUpdater::Resource>(
       new Resource(this, PrioritizedResource::Create(manager)));
 }
 
 void BitmapContentLayerUpdater::PrepareToUpdate(
     gfx::Rect content_rect,
     gfx::Size tile_size,
     float contents_width_scale,
     float contents_height_scale,
     gfx::Rect* resulting_opaque_rect) {
   devtools_instrumentation::ScopedLayerTask paint_layer(
       devtools_instrumentation::kPaintLayer, layer_id_);
   if (canvas_size_ != content_rect.size()) {
     devtools_instrumentation::ScopedLayerTask paint_setup(
         devtools_instrumentation::kPaintSetup, layer_id_);
     canvas_size_ = content_rect.size();
     canvas_ = skia::AdoptRef(skia::CreateBitmapCanvas(
-        canvas_size_.width(), canvas_size_.height(), opaque_));
+        canvas_size_.width(), canvas_size_.height(), layer_is_opaque_));
   }
 
   base::TimeTicks start_time =
       rendering_stats_instrumentation_->StartRecording();
   PaintContents(canvas_.get(),
                 content_rect,
                 contents_width_scale,
                 contents_height_scale,
                 resulting_opaque_rect);
   base::TimeDelta duration =
@@ skipping 20 matching lines @@
   else
     queue->AppendFullUpload(upload);
 }
 
 void BitmapContentLayerUpdater::ReduceMemoryUsage() {
   canvas_.clear();
   canvas_size_ = gfx::Size();
 }
 
 void BitmapContentLayerUpdater::SetOpaque(bool opaque) {
-  if (opaque != opaque_) {
+  if (opaque != layer_is_opaque_) {
     canvas_.clear();
     canvas_size_ = gfx::Size();
   }
-  opaque_ = opaque;
+
+  ContentLayerUpdater::SetOpaque(opaque);
 }
 
 }  // namespace cc