Don't create render passes for transparent images.

cc/layer_tree_host_common.cc

Index: cc/layer_tree_host_common.cc
diff --git a/cc/layer_tree_host_common.cc b/cc/layer_tree_host_common.cc
index ca7d45050f85c0857e5f88a4def5818ef1b5374e..7c68f80c5d2280282bfaafccf049e389514d8da3 100644
--- a/cc/layer_tree_host_common.cc
+++ b/cc/layer_tree_host_common.cc
@@ -259,7 +259,7 @@ static bool subtreeShouldRenderToSeparateSurface(LayerType* layer, bool axisAlig
         return true;
 
     // If the layer has opacity != 1 and does not have a preserves-3d transform style.
-    if (layer->opacity() != 1 && !layer->preserves3D() && descendantDrawsContent)
+    if (layer->opacity() != 1 && !layer->preserves3D() && layer->drawsContent() && descendantDrawsContent)
         return true;
 
     return false;
@@ -484,17 +484,17 @@ static void calculateDrawTransformsInternal(LayerType* layer, const WebTransform
 
     gfx::Rect clipRectForSubtree;
     bool subtreeShouldBeClipped = false;
-    
+
     float drawOpacity = layer->opacity();
     bool drawOpacityIsAnimating = layer->opacityIsAnimating();
-    if (layer->parent() && layer->parent()->preserves3D()) {
+    if (layer->parent()) {
         drawOpacity *= layer->parent()->drawOpacity();
         drawOpacityIsAnimating |= layer->parent()->drawOpacityIsAnimating();
     }
 
     bool animatingTransformToTarget = layer->transformIsAnimating();
     bool animatingTransformToScreen = animatingTransformToTarget;
-    if (layer->parent()) {
+    if (layer->parent() && !layer->parent()->renderSurface()) {

[shawnsingh, 2012/11/26 19:03:08]

I think our discussion also applies to this if-statement, too, right?   i.e. the
XXXIsAnimating() accessors are computed properties that are reparented by a
surface, not properties given by the user of the compositor.

[danakj, 2012/11/26 19:09:44]

Yes, the check was added to the wrong if statement here. It would break the
screenSpaceTransformIsAnimating case here.

         animatingTransformToTarget |= layer->parent()->drawTransformIsAnimating();
         animatingTransformToScreen |= layer->parent()->screenSpaceTransformIsAnimating();
     }