detect when we can filter bitmaps/images directly, w/o a tmp layer

include/core/SkCanvas.h

Index: include/core/SkCanvas.h
diff --git a/include/core/SkCanvas.h b/include/core/SkCanvas.h
index 53f6dda88b090c5734a7e7104925ae0749bb76d9..cd6421beb184c75c7879aac2ecc9e10e1504a6e1 100644
--- a/include/core/SkCanvas.h
+++ b/include/core/SkCanvas.h
@@ -1428,6 +1428,10 @@ private:
      */
     bool wouldOverwriteEntireSurface(const SkRect*, const SkPaint*, ShaderOverrideOpacity) const;
 
+    /**
+     *  Returns true if the paint's imagefilter can be invoked directly, without needed a layer.
+     */
+    bool canDrawBitmapAsSprite(SkScalar x, SkScalar y, int w, int h, const SkPaint&);
 
     /*  These maintain a cache of the clip bounds in local coordinates,
         (converted to 2s-compliment if floats are slow).