Add auto purging for SkPicture-related Ganesh resources (esp. layers)

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
 
@@ skipping 320 matching lines @@
     SkDeviceProperties fLeakyProperties;
 
     /**
      *  PRIVATE / EXPERIMENTAL -- do not call
      *  Construct an acceleration object and attach it to 'picture'
      */
     virtual void EXPERIMENTAL_optimize(const SkPicture* picture);
 
     /**
      *  PRIVATE / EXPERIMENTAL -- do not call
-     *  Purge all discardable optimization information for 'picture'. If
-     *  picture is NULL then purge discardable information for all pictures.
-     */
-    virtual void EXPERIMENTAL_purge(const SkPicture* picture);
-
-    /**
-     *  PRIVATE / EXPERIMENTAL -- do not call
      *  This entry point gives the backend an opportunity to take over the rendering
      *  of 'picture'. If optimization data is available (due to an earlier
      *  'optimize' call) this entry point should make use of it and return true
      *  if all rendering has been done. If false is returned, SkCanvas will
      *  perform its own rendering pass. It is acceptable for the backend
      *  to perform some device-specific warm up tasks and then let SkCanvas
      *  perform the main rendering loop (by return false from here).
      */
     virtual bool EXPERIMENTAL_drawPicture(SkCanvas* canvas, const SkPicture* picture);
 
@@ skipping 31 matching lines @@
     SkMetaData* fMetaData;
 
 #ifdef SK_DEBUG
     bool        fAttachedToCanvas;
 #endif
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif