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

src/image/SkImage_Gpu.h

Index: src/image/SkImage_Gpu.h
diff --git a/src/image/SkImage_Gpu.h b/src/image/SkImage_Gpu.h
index ff3b12e668d4170f6553dc662afc627d759c1860..bd8abd24e234b51b563f65663aa7c9f53fe541ef 100644
--- a/src/image/SkImage_Gpu.h
+++ b/src/image/SkImage_Gpu.h
@@ -50,6 +50,8 @@ public:
         return SkSurface::NewRenderTarget(fTexture->getContext(), SkSurface::kNo_Budgeted, info);
     }
 
+    bool asBitmapForImageFilters(SkBitmap* bitmap) const override;
+
 private:
     SkAutoTUnref<GrTexture>     fTexture;
     const SkAlphaType           fAlphaType;