Don't create render passes for transparent images.

cc/layer.cc

Index: cc/layer.cc
diff --git a/cc/layer.cc b/cc/layer.cc
index c7b7ebc503b02e3e7190777985bf67d880a685e7..242ad765ed55ec51053e471195c8530c80ad0e2e 100644
--- a/cc/layer.cc
+++ b/cc/layer.cc
@@ -698,13 +698,17 @@ void Layer::createRenderSurface()
     setRenderTarget(this);
 }
 
-bool Layer::descendantDrawsContent()
+int Layer::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;
 }
 
 int Layer::id() const