Add SkGpuDevice::asSpecial entry point

src/gpu/SkGpuDevice.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 SkGpuDevice_DEFINED
 #define SkGpuDevice_DEFINED
 
@@ skipping 113 matching lines @@
 
     void drawImage(const SkDraw&, const SkImage*, SkScalar x, SkScalar y, const SkPaint&) override;
     void drawImageRect(const SkDraw&, const SkImage*, const SkRect* src, const SkRect& dst,
                        const SkPaint&, SkCanvas::SrcRectConstraint) override;
 
     void drawImageNine(const SkDraw& draw, const SkImage* image, const SkIRect& center,
                        const SkRect& dst, const SkPaint& paint) override;
     void drawBitmapNine(const SkDraw& draw, const SkBitmap& bitmap, const SkIRect& center,
                         const SkRect& dst, const SkPaint& paint) override;
 
+    sk_sp<SkSpecialImage> asSpecial();
     void drawSpecial(const SkDraw& draw, SkSpecialImage*,
                      int left, int top, const SkPaint& paint);
 
     void flush() override;
 
     void onAttachToCanvas(SkCanvas* canvas) override;
     void onDetachFromCanvas() override;
 
     const SkBitmap& onAccessBitmap() override;
     bool onAccessPixels(SkPixmap*) override;
@@ skipping 125 matching lines @@
 
     void drawSpriteWithFilter(const SkDraw&, const SkBitmap&, int x, int y,
                               const SkPaint&) override;
 
     friend class GrAtlasTextContext;
     friend class SkSurface_Gpu;      // for access to surfaceProps
     typedef SkBaseDevice INHERITED;
 };
 
 #endif