Implement SkBaseDevice snapshot support

include/core/SkDevice.h

 /*
  * Copyright 2010 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkDevice_DEFINED
 #define SkDevice_DEFINED
 
 #include "SkRefCnt.h"
 #include "SkBitmap.h"
 #include "SkCanvas.h"
 #include "SkColor.h"
 #include "SkImageFilter.h"
 
 class SkClipStack;
 class SkDraw;
 class SkDrawFilter;
+class SkImage;
 struct SkIRect;
 class SkMatrix;
 class SkMetaData;
 class SkRegion;
 struct SkDeviceProperties;
 class GrRenderTarget;
 
 class SK_API SkBaseDevice : public SkRefCnt {
 public:
     SK_DECLARE_INST_COUNT(SkBaseDevice)
@@ skipping 87 matching lines @@
      * possibly from SkCanvas' dtor.
      */
     virtual void onDetachFromCanvas() {
         SkASSERT(fAttachedToCanvas);
         this->unlockPixels();
 #ifdef SK_DEBUG
         fAttachedToCanvas = false;
 #endif
     };
 
+    virtual SkImage* newImageSnapshot() { return NULL; }
+
+    /** This makes the contents of this device undefined.
+     * See SkCanvas::discard()
+     */
+    virtual void discard() { }
+
 protected:
     enum TileUsage {
         kPossible_TileUsage,    //!< the created device may be drawn tiled
         kNever_TileUsage,       //!< the created device will never be drawn tiled
     };
 
     struct TextFlags {
         uint32_t    fFlags;     // SkPaint::getFlags()
     };
 
@@ skipping 225 matching lines @@
     friend class SkDeviceImageFilterProxy;
     friend class SkDeferredDevice;    // for newSurface
     friend class SkNoPixelsBitmapDevice;
 
     friend class SkSurface_Raster;
 
     // used to change the backend's pixels (and possibly config/rowbytes)
     // but cannot change the width/height, so there should be no change to
     // any clip information.
     // TODO: move to SkBitmapDevice
-    virtual void replaceBitmapBackendForRasterSurface(const SkBitmap&) {}
+    virtual void replaceBitmapBackend(const SkBitmap&) {}
 
     virtual bool forceConservativeRasterClip() const { return false; }
 
     // just called by SkCanvas when built as a layer
     void setOrigin(int x, int y) { fOrigin.set(x, y); }
 
     /** Causes any deferred drawing to the device to be completed.
      */
     virtual void flush() {}
 
     virtual SkImageFilter::Cache* getImageFilterCache() { return NULL; }
 
     SkIPoint    fOrigin;
     SkMetaData* fMetaData;
     SkDeviceProperties* fLeakyProperties;   // will always exist.
 
 #ifdef SK_DEBUG
     bool        fAttachedToCanvas;
 #endif
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif