Don't create render passes for transparent images.

cc/layer_tree_host_impl_unittest.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/layer_tree_host_impl.h"
 
 #include <cmath>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 2351 matching lines @@
     root->setDrawsContent(false);
     root->renderSurface()->setContentRect(gfx::Rect(gfx::Point(), gfx::Size(rootRect.width(), rootRect.height())));
 
     child->setAnchorPoint(gfx::PointF(0, 0));
     child->setPosition(gfx::PointF(childRect.x(), childRect.y()));
     child->setOpacity(0.5f);
     child->setBounds(gfx::Size(childRect.width(), childRect.height()));
     child->setContentBounds(child->bounds());
     child->setVisibleContentRect(childRect);
     child->setDrawsContent(false);
+    child->setForceRenderSurface(true);
 
     grandChild->setAnchorPoint(gfx::PointF(0, 0));
     grandChild->setPosition(gfx::Point(grandChildRect.x(), grandChildRect.y()));
     grandChild->setBounds(gfx::Size(grandChildRect.width(), grandChildRect.height()));
     grandChild->setContentBounds(grandChild->bounds());
     grandChild->setVisibleContentRect(grandChildRect);
     grandChild->setDrawsContent(true);
 
     child->addChild(grandChild.Pass());
     root->addChild(child.Pass());
@@ skipping 729 matching lines @@
     root->setDrawsContent(true);
     layerTreeHostImpl->setRootLayer(root.Pass());
 
     addDrawingLayerTo(rootPtr, 2, gfx::Rect(10, 10, rootSize.width(), rootSize.height()), &intermediateLayerPtr);
     intermediateLayerPtr->setDrawsContent(false); // only children draw content
 
     // Surface layer is the layer that changes its opacity
     // It will contain other layers that draw content.
     addDrawingLayerTo(intermediateLayerPtr, 3, gfx::Rect(10, 10, rootSize.width(), rootSize.height()), &surfaceLayerPtr);
     surfaceLayerPtr->setDrawsContent(false); // only children draw content
-    surfaceLayerPtr->setOpacity(0.5f); // This will cause it to have a surface
+    surfaceLayerPtr->setOpacity(0.5f);
+    surfaceLayerPtr->setForceRenderSurface(true); // This will cause it to have a surface
 
     // Child of the surface layer will produce some quads
     addDrawingLayerTo(surfaceLayerPtr, 4, gfx::Rect(5, 5, rootSize.width() - 25, rootSize.height() - 25), &childPtr);
 }
 
 class GLRendererWithReleaseTextures : public GLRenderer {
 public:
     using GLRenderer::releaseRenderPassTextures;
 };
 
@@ skipping 23 matching lines @@
     root->setContentBounds(rootSize);
     root->setDrawsContent(true);
     root->setMasksToBounds(true);
     myHostImpl->setRootLayer(root.Pass());
 
     addDrawingLayerTo(rootPtr, 3, gfx::Rect(0, 0, rootSize.width(), rootSize.height()), &surfaceLayerPtr);
     surfaceLayerPtr->setDrawsContent(false);
 
     // Surface layer is the layer that changes its opacity
     // It will contain other layers that draw content.
-    surfaceLayerPtr->setOpacity(0.5f); // This will cause it to have a surface
+    surfaceLayerPtr->setOpacity(0.5f);
+    surfaceLayerPtr->setForceRenderSurface(true); // This will cause it to have a surface
 
     addDrawingLayerTo(surfaceLayerPtr, 4, gfx::Rect(0, 0, 100, 3), 0);
     addDrawingLayerTo(surfaceLayerPtr, 5, gfx::Rect(0, 97, 100, 3), 0);
 
     // Rotation will put part of the child ouside the bounds of the root layer.
     // Nevertheless, the child layers should be drawn.
     WebTransformationMatrix transform = surfaceLayerPtr->transform();
     transform.translate(50, 50);
     transform.rotate(35);
     transform.translate(-50, -50);
@@ skipping 1693 matching lines @@
 {
     pinchZoomPanViewportAndScrollBoundaryTest(2);
 }
 
 INSTANTIATE_TEST_CASE_P(LayerTreeHostImplTests,
                         LayerTreeHostImplTest,
                         ::testing::Values(false, true));
 
 }  // namespace
 }  // namespace cc