Make SkBitmap::CopyTo respect requested dst color type when bitmap is texture backed.

include/gpu/SkGrPixelRef.h

 /*
  * Copyright 2010 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkGrPixelRef_DEFINED
 #define SkGrPixelRef_DEFINED
 
@@ skipping 31 matching lines @@
      * Constructs a pixel ref around a GrSurface.
      */
     SkGrPixelRef(const SkImageInfo&, GrSurface*);
     virtual ~SkGrPixelRef();
 
     // override from SkPixelRef
     GrTexture* getTexture() override;
 
 protected:
     // overrides from SkPixelRef
-    bool onReadPixels(SkBitmap* dst, const SkIRect* subset) override;
+    bool onReadPixels(SkBitmap* dst, SkColorType, const SkIRect* subset) override;
     SkPixelRef* deepCopy(SkColorType, SkColorProfileType,
                          const SkIRect* subset) override;
     void onNotifyPixelsChanged() override;
 
 private:
     GrSurface*  fSurface;
     typedef SkROLockPixelsPixelRef INHERITED;
 };
 
 #endif