[2/5] Disable transformed rasterization if layer is opaque

cc/layers/picture_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/picture_layer.h"
 
 #include "base/auto_reset.h"
 #include "base/trace_event/trace_event.h"
 #include "cc/blimp/client_picture_cache.h"
 #include "cc/blimp/engine_picture_cache.h"
@@ skipping 84 matching lines @@
     recording_source_->SetNeedsDisplayRect(layer_rect);
   Layer::SetNeedsDisplayRect(layer_rect);
 }
 
 bool PictureLayer::Update() {
   update_source_frame_number_ = layer_tree_host()->SourceFrameNumber();
   bool updated = Layer::Update();
 
   gfx::Size layer_size = paint_properties().bounds;
 
-  recording_source_->SetBackgroundColor(SafeOpaqueBackgroundColor());
+  recording_source_->SetBackgroundColor(UseTransformedRasterization() ? SK_ColorTRANSPARENT : SafeOpaqueBackgroundColor());

[enne (OOO), 2017/01/03 22:53:07]

This needs a comment as to why this is the case.

[trchen, 2017/01/14 00:46:46]

Done.

   recording_source_->SetRequiresClear(
       !contents_opaque() &&
       !picture_layer_inputs_.client->FillsBoundsCompletely());
 
   TRACE_EVENT1("cc", "PictureLayer::Update", "source_frame_number",
                layer_tree_host()->SourceFrameNumber());
   devtools_instrumentation::ScopedLayerTreeTask update_layer(
       devtools_instrumentation::kUpdateLayer, id(), layer_tree_host()->GetId());
 
   // UpdateAndExpandInvalidation will give us an invalidation that covers
@@ skipping 175 matching lines @@
     return false;
 
   return true;
 }
 
 const DisplayItemList* PictureLayer::GetDisplayItemList() {
   return picture_layer_inputs_.display_list.get();
 }
 
 }  // namespace cc