Don't create render passes for transparent images.

cc/layer.h

Index: cc/layer.h
diff --git a/cc/layer.h b/cc/layer.h
index ef75286debfb859737418d896d3863c6fe049125..2119eec37411ecdc2f74cf6c63efaa461304bf33 100644
--- a/cc/layer.h
+++ b/cc/layer.h
@@ -266,9 +266,6 @@ public:
     void setBoundsContainPageScale(bool);
     bool boundsContainPageScale() const { return m_boundsContainPageScale; }
 
-    // Returns true if any of the layer's descendants has content to draw.
-    bool descendantDrawsContent();

[danakj, 2012/11/27 01:52:16]

You should replace this with numDescendantsThatDrawContent() and have the
ubercomp layer return the number of sharedQuadStates it owns - 1.

-
     LayerTreeHost* layerTreeHost() const { return m_layerTreeHost; }
 
     // Set the priority of all desired textures in this layer.