cc: Don't clear transparent piles to an opaque color

cc/layers/layer_impl.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/layers/layer_impl.h"
 
 #include "base/debug/trace_event.h"
 #include "base/stringprintf.h"
 #include "cc/animation/animation_registrar.h"
 #include "cc/animation/scrollbar_animation_controller.h"
@@ skipping 672 matching lines @@
 }
 
 void LayerImpl::SetBackgroundColor(SkColor background_color) {
   if (background_color_ == background_color)
     return;
 
   background_color_ = background_color;
   NoteLayerPropertyChanged();
 }
 
+SkColor LayerImpl::SafeOpaqueBackgroundColor() const {
+  SkColor color = background_color();
+  if (SkColorGetA(color) == 255 && !contents_opaque()) {
+    color = SK_ColorTRANSPARENT;
+  } else if (SkColorGetA(color) != 255 && contents_opaque()) {
+    for (const LayerImpl* layer = parent(); layer;
+         layer = layer->parent()) {
+      color = layer->background_color();
+      if (SkColorGetA(color) == 255)
+        break;
+    }
+    if (SkColorGetA(color) != 255)
+      color = layer_tree_impl()->background_color();
+    if (SkColorGetA(color) != 255)
+      color = SkColorSetA(color, 255);
+  }
+  return color;
+}
+
 void LayerImpl::SetFilters(const WebKit::WebFilterOperations& filters) {
   if (filters_ == filters)
     return;
 
   DCHECK(!filter_);
   filters_ = filters;
   NoteLayerPropertyChangedForSubtree();
 }
 
 void LayerImpl::SetBackgroundFilters(
@@ skipping 444 matching lines @@
 
 size_t LayerImpl::GPUMemoryUsageInBytes() const { return 0; }
 
 scoped_ptr<base::Value> LayerImpl::AsValue() const {
   scoped_ptr<base::DictionaryValue> state(new base::DictionaryValue());
   AsValueInto(state.get());
   return state.PassAs<base::Value>();
 }
 
 }  // namespace cc