Don't create render passes for transparent images.

cc/layer_impl.cc

Index: cc/layer_impl.cc
diff --git a/cc/layer_impl.cc b/cc/layer_impl.cc
index 81bc49f01aafb4a2ea926f0412e3764a5c786d8a..42391038db4d400dc257977e47ab13d3a7a0f123 100644
--- a/cc/layer_impl.cc
+++ b/cc/layer_impl.cc
@@ -112,13 +112,17 @@ void LayerImpl::createRenderSurface()
     setRenderTarget(this);
 }
 
-bool LayerImpl::descendantDrawsContent()
+int LayerImpl::descendantsDrawContent()
 {
+    int result = 0;
     for (size_t i = 0; i < m_children.size(); ++i) {
-        if (m_children[i]->drawsContent() || m_children[i]->descendantDrawsContent())
-            return true;
+        if (m_children[i]->drawsContent())
+            ++result;
+        result += m_children[i]->descendantsDrawContent();
+        if (result > 1)
+            return result;
     }
-    return false;
+    return result;
 }
 
 scoped_ptr<SharedQuadState> LayerImpl::createSharedQuadState() const