Don't create render passes for transparent images.

cc/layer_tree_host_common_unittest.cc

Index: cc/layer_tree_host_common_unittest.cc
diff --git a/cc/layer_tree_host_common_unittest.cc b/cc/layer_tree_host_common_unittest.cc
index 456ea52f1fafac554620061135916567e46636b6..06c266b549698d7028c43d180cde75c13185e920 100644
--- a/cc/layer_tree_host_common_unittest.cc
+++ b/cc/layer_tree_host_common_unittest.cc
@@ -341,6 +341,7 @@ TEST(LayerTreeHostCommonTest, verifyTransformsForSingleRenderSurface)
 
     // Child is set up so that a new render surface should be created.
     child->setOpacity(0.5);
+    child->setForceRenderSurface(true);
 
     WebTransformationMatrix parentLayerTransform;
     parentLayerTransform.scale3d(1, 0.9, 1);
@@ -1369,6 +1370,7 @@ TEST(LayerTreeHostCommonTest, verifyClipRectCullsRenderSurfaces)
 
     child->setMasksToBounds(true);
     child->setOpacity(0.4f);
+    child->setForceRenderSurface(true);
     grandChild->setOpacity(0.5);
     greatGrandChild->setOpacity(0.4f);
 
@@ -1415,7 +1417,9 @@ TEST(LayerTreeHostCommonTest, verifyClipRectCullsSurfaceWithoutVisibleContent)
 
     parent->setMasksToBounds(true);
     child->setOpacity(0.4f);
+    child->setForceRenderSurface(true);
     grandChild->setOpacity(0.4f);
+    grandChild->setForceRenderSurface(true);
 
     std::vector<scoped_refptr<Layer> > renderSurfaceLayerList;
     int dummyMaxTextureSize = 512;
@@ -1643,10 +1647,15 @@ TEST(LayerTreeHostCommonTest, verifyClipRectIsPropagatedCorrectlyToSurfaces)
 
     // Force everyone to be a render surface.
     child->setOpacity(0.4f);
+    child->setForceRenderSurface(true);
     grandChild1->setOpacity(0.5);
+    grandChild1->setForceRenderSurface(true);
     grandChild2->setOpacity(0.5);
+    grandChild2->setForceRenderSurface(true);
     grandChild3->setOpacity(0.5);
+    grandChild3->setForceRenderSurface(true);
     grandChild4->setOpacity(0.5);
+    grandChild4->setForceRenderSurface(true);
 
     std::vector<scoped_refptr<Layer> > renderSurfaceLayerList;
     int dummyMaxTextureSize = 512;
@@ -4625,5 +4634,26 @@ TEST(LayerTreeHostCommonTest, verifySubtreeSearch)
     EXPECT_EQ(0, LayerTreeHostCommon::findLayerInSubtree(root.get(), nonexistentId));
 }
 
+TEST(LayerTreeHostCommonTest, verifyTransparentImageRenderSurfaceCreation)
+{
+    // Make sure that we don't create render passes for transparent images.

[jamesr, 2012/11/27 01:34:46]

this test doesn't appear to have anything to do with image layers in particular,
it's more about opacity with exactly 1 descendant that draws - could you refine
the comment + test name?

+    scoped_refptr<Layer> root = Layer::create();
+    scoped_refptr<Layer> child = Layer::create();
+    scoped_refptr<LayerWithForcedDrawsContent> grandChild = make_scoped_refptr(new LayerWithForcedDrawsContent());
+
+    const WebTransformationMatrix identityMatrix;
+    setLayerPropertiesForTesting(root.get(), identityMatrix, identityMatrix, gfx::PointF(), gfx::PointF(), gfx::Size(100, 100), false);
+    setLayerPropertiesForTesting(child.get(), identityMatrix, identityMatrix, gfx::PointF(), gfx::PointF(), gfx::Size(10, 10), false);
+    setLayerPropertiesForTesting(grandChild.get(), identityMatrix, identityMatrix, gfx::PointF(), gfx::PointF(), gfx::Size(10, 10), false);
+
+    root->addChild(child);
+    child->addChild(grandChild);
+    child->setOpacity(0.5f);
+
+    executeCalculateDrawTransformsAndVisibility(root.get());
+
+    EXPECT_FALSE(child->renderSurface());
+}
+
 }  // namespace
 }  // namespace cc