Implement SkBaseDevice snapshot support

src/image/SkSurface_Base.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkSurface_Base_DEFINED
 #define SkSurface_Base_DEFINED
 
@@ skipping 29 matching lines @@
      *  Default implementation:
      *
      *  image = this->newImageSnapshot();
      *  if (image) {
      *      image->draw(canvas, ...);
      *      image->unref();
      *  }
      */
     virtual void onDraw(SkCanvas*, SkScalar x, SkScalar y, const SkPaint*);
 
-    /**
-     * Called as a performance hint when the Surface is allowed to make it's contents
-     * undefined.
-     */
-    virtual void onDiscard() {}
+    inline SkCanvas* getCachedCanvas();
 
-    /**
-     *  If the surface is about to change, we call this so that our subclass
-     *  can optionally fork their backend (copy-on-write) in case it was
-     *  being shared with the cachedImage.
-     */
-    virtual void onCopyOnWrite(ContentChangeMode) = 0;
-
-    inline SkCanvas* getCachedCanvas();
-    inline SkImage* getCachedImage(Budgeted);
-
-    // called by SkSurface to compute a new genID
+protected:
+    // Must be called by the subclasses to compute a new genID.
     uint32_t newGenerationID();
 
 private:
     SkCanvas*   fCachedCanvas;
-    SkImage*    fCachedImage;
 
-    void aboutToDraw(ContentChangeMode mode);
-    friend class SkCanvas;
     friend class SkSurface;
-
     typedef SkSurface INHERITED;
 };
 
 SkCanvas* SkSurface_Base::getCachedCanvas() {
     if (NULL == fCachedCanvas) {
         fCachedCanvas = this->onNewCanvas();
-        if (fCachedCanvas) {
-            fCachedCanvas->setSurfaceBase(this);
-        }
     }
     return fCachedCanvas;
 }
 
-SkImage* SkSurface_Base::getCachedImage(Budgeted budgeted) {
-    if (NULL == fCachedImage) {
-        fCachedImage = this->onNewImageSnapshot(budgeted);
-        SkASSERT(!fCachedCanvas || fCachedCanvas->getSurfaceBase() == this);
-    }
-    return fCachedImage;
-}
-
 #endif