Don't create render passes for transparent images.

cc/delegated_renderer_layer_impl.h

 // 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.
 
 #ifndef CC_DELEGATED_RENDERER_LAYER_IMPL_H_
 #define CC_DELEGATED_RENDERER_LAYER_IMPL_H_
 
 #include "cc/cc_export.h"
 #include "cc/layer_impl.h"
 #include "cc/scoped_ptr_vector.h"
 
 namespace cc {
 
 class CC_EXPORT DelegatedRendererLayerImpl : public LayerImpl {
 public:
     static scoped_ptr<DelegatedRendererLayerImpl> create(int id) { return make_scoped_ptr(new DelegatedRendererLayerImpl(id)); }
     virtual ~DelegatedRendererLayerImpl();
 
-    virtual bool descendantDrawsContent() OVERRIDE;
     virtual bool hasContributingDelegatedRenderPasses() const OVERRIDE;
 
     // This gives ownership of the RenderPasses to the layer.
     void setRenderPasses(ScopedPtrVector<RenderPass>&);
     void clearRenderPasses();
 
     virtual void didLoseContext() OVERRIDE;
 
     virtual RenderPass::Id firstContributingRenderPassId() const OVERRIDE;
     virtual RenderPass::Id nextContributingRenderPassId(RenderPass::Id) const OVERRIDE;
@@ skipping 10 matching lines @@
 
     virtual const char* layerTypeAsString() const OVERRIDE;
 
     ScopedPtrVector<RenderPass> m_renderPassesInDrawOrder;
     base::hash_map<RenderPass::Id, int> m_renderPassesIndexById;
 };
 
 }
 
 #endif  // CC_DELEGATED_RENDERER_LAYER_IMPL_H_