add heuristic to pour small pictures into recordings, rather than ref'ing

include/core/SkCanvas.h

Index: include/core/SkCanvas.h
diff --git a/include/core/SkCanvas.h b/include/core/SkCanvas.h
index dcbff3f60b6030f619358539d0f2b798dc0d6416..9282267721eff192e66efd7d2cf2ace63cb9a9e0 100644
--- a/include/core/SkCanvas.h
+++ b/include/core/SkCanvas.h
@@ -951,7 +951,9 @@ public:
         @param picture The recorded drawing commands to playback into this
                        canvas.
     */
-    void drawPicture(const SkPicture* picture);
+    void drawPicture(const SkPicture* picture) {
+        this->drawPicture(picture, NULL, NULL);
+    }
 
     /**
      *  Draw the picture into this canvas.