Don't create render passes for transparent images.

cc/layer_iterator_unittest.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/layer_iterator.h"
 
 #include "cc/layer.h"
 #include "cc/layer_tree_host_common.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ skipping 196 matching lines @@
     scoped_refptr<TestLayer> root221 = TestLayer::create();
     scoped_refptr<TestLayer> root231 = TestLayer::create();
 
     rootLayer->createRenderSurface();
     rootLayer->renderSurface()->setContentRect(gfx::Rect(gfx::Point(), rootLayer->bounds()));
 
     rootLayer->addChild(root1);
     rootLayer->addChild(root2);
     rootLayer->addChild(root3);
     root2->setDrawsContent(false);
-    root2->setOpacity(0.5); // Force the layer to own a new surface.
+    root2->setOpacity(0.5);
+    root2->setForceRenderSurface(true); // Force the layer to own a new surface.
     root2->addChild(root21);
     root2->addChild(root22);
     root2->addChild(root23);
     root22->setOpacity(0.5);
     root22->addChild(root221);
     root23->setOpacity(0.5);
     root23->addChild(root231);
 
     std::vector<scoped_refptr<Layer> > renderSurfaceLayerList;
     LayerTreeHostCommon::calculateDrawTransforms(rootLayer.get(), rootLayer->bounds(), 1, 1, 256, renderSurfaceLayerList);
@@ skipping 16 matching lines @@
     EXPECT_COUNT(root21, -1, -1, 9);
     EXPECT_COUNT(root22, 7, 8, 6);
     EXPECT_COUNT(root221, -1, -1, 5);
     EXPECT_COUNT(root23, 3, 4, 2);
     EXPECT_COUNT(root231, -1, -1, 1);
     EXPECT_COUNT(root3, -1, -1, 0);
 }
 
 }  // namespace
 }  // namespace cc