Add refcnting to SkClipStack on SkCanvas

include/core/SkCanvas.h

Index: include/core/SkCanvas.h
diff --git a/include/core/SkCanvas.h b/include/core/SkCanvas.h
index d929439083055fa49bc3f2cd3ee3b810dd970d45..53ca92ee959d9adfd233ad58f53d7c4978bfe544 100644
--- a/include/core/SkCanvas.h
+++ b/include/core/SkCanvas.h
@@ -1081,7 +1081,7 @@ public:
      *  @return the current clip stack ("list" of individual clip elements)
      */
     const SkClipStack* getClipStack() const {
-        return &fClipStack;
+        return fClipStack;
     }
 
     typedef SkCanvasClipVisitor ClipVisitor;
@@ -1243,7 +1243,7 @@ protected:
 private:
     class MCRec;
 
-    SkClipStack fClipStack;
+    SkAutoTUnref<SkClipStack> fClipStack;
     SkDeque     fMCStack;
     // points to top of stack
     MCRec*      fMCRec;