cc: Block the main thread for texture layers during impl-side painting

cc/layer.h

Index: cc/layer.h
diff --git a/cc/layer.h b/cc/layer.h
index e7df4c08417438213d18838adcc177e5d440b765..fab8faeedf623f2856a41e619fb994073cd05f4b 100644
--- a/cc/layer.h
+++ b/cc/layer.h
@@ -288,6 +288,8 @@ public:
     // compatible with the main thread running freely, such as a double-buffered
     // canvas that doesn't want to be triple-buffered across all three trees.
     virtual bool blocksPendingCommit() const;
+    // Returns true if anything in this tree blocksPendingCommit.
+    bool blocksPendingCommitRecursive() const;
 
 protected:
     friend class LayerImpl;