Add SkNVRefCnt, prune down SkPicture's size

include/core/SkPicture.h

Index: include/core/SkPicture.h
diff --git a/include/core/SkPicture.h b/include/core/SkPicture.h
index eee1ea840141bf5145e93893ad1824eb1aa38512..70901d5ab8d220f34d8b8450cc63f70ccb6a8d9b 100644
--- a/include/core/SkPicture.h
+++ b/include/core/SkPicture.h
@@ -40,7 +40,7 @@ namespace SkRecords {
     The SkPicture class records the drawing commands made to a canvas, to
     be played back at a later time.
 */
-class SK_API SkPicture : public SkRefCnt {
+class SK_API SkPicture : public SkNVRefCnt<SkPicture> {
 public:
     SK_DECLARE_INST_COUNT(SkPicture)
 
@@ -104,7 +104,7 @@ public:
      */
     static SkPicture* CreateFromBuffer(SkReadBuffer&);
 
-    virtual ~SkPicture();
+    ~SkPicture();
 
     /** Replays the drawing commands on the specified canvas. Note that
         this has the effect of unfurling this picture into the destination