Don't create render passes for transparent images.

cc/delegated_renderer_layer_impl.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/delegated_renderer_layer_impl.h"
 
 #include "cc/append_quads_data.h"
 #include "cc/math_util.h"
 #include "cc/quad_sink.h"
 #include "cc/render_pass_draw_quad.h"
 #include "cc/render_pass_sink.h"
 
 namespace cc {
 
 DelegatedRendererLayerImpl::DelegatedRendererLayerImpl(int id)
     : LayerImpl(id)
 {
 }
 
 DelegatedRendererLayerImpl::~DelegatedRendererLayerImpl()
 {
     clearRenderPasses();
 }
 
-bool DelegatedRendererLayerImpl::descendantDrawsContent()
+int DelegatedRendererLayerImpl::descendantsDrawContent()
 {
     // FIXME: This could possibly return false even though there are some
     // quads present as they could all be from a single layer (or set of
     // layers without children). If this happens, then make a test that
     // ensures the opacity is being changed on quads in the root RenderPass
     // when this layer doesn't own a RenderSurfaceImpl.
-    return !m_renderPassesInDrawOrder.isEmpty();
+    return m_renderPassesInDrawOrder.isEmpty() ? 0 : 2;
 }
 
 bool DelegatedRendererLayerImpl::hasContributingDelegatedRenderPasses() const
 {
     // The root RenderPass for the layer is merged with its target
     // RenderPass in each frame. So we only have extra RenderPasses
     // to merge when we have a non-root RenderPass present.
     return m_renderPassesInDrawOrder.size() > 1;
 }
 
@@ skipping 129 matching lines @@
         quadSink.append(copyQuad.Pass(), appendQuadsData);
     }
 }
 
 const char* DelegatedRendererLayerImpl::layerTypeAsString() const
 {
     return "DelegatedRendererLayer";
 }
 
 }  // namespace cc