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

src/image/SkImage_Gpu.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImage_Gpu_DEFINED
 #define SkImage_Gpu_DEFINED
 
@@ skipping 32 matching lines @@
     bool isOpaque() const override;
     bool onReadPixels(const SkImageInfo&, void* dstPixels, size_t dstRowBytes,
                       int srcX, int srcY, CachingHint) const override;
     SkImage* onApplyFilter(SkImageFilter*, SkIPoint* offset,
                            bool forceResultToOriginalSize) const override;
 
     SkSurface* onNewSurface(const SkImageInfo& info) const override {
         return SkSurface::NewRenderTarget(fTexture->getContext(), SkSurface::kNo_Budgeted, info);
     }
 
+    bool asBitmapForImageFilters(SkBitmap* bitmap) const override;
+
 private:
     SkAutoTUnref<GrTexture>     fTexture;
     const SkAlphaType           fAlphaType;
     const SkSurface::Budgeted   fBudgeted;
     mutable SkAtomic<bool>      fAddedRasterVersionToCache;
 
 
     typedef SkImage_Base INHERITED;
 };
 
 #endif