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

src/core/SkCanvas.cpp

 /*
  * Copyright 2008 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.
  */
 
 
 #include "SkCanvas.h"
 #include "SkBitmapDevice.h"
@@ skipping 2368 matching lines @@
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 void SkCanvas::EXPERIMENTAL_optimize(const SkPicture* picture) {
     SkBaseDevice* device = this->getDevice();
     if (NULL != device) {
         device->EXPERIMENTAL_optimize(picture);
     }
 }
 
-void SkCanvas::EXPERIMENTAL_purge(const SkPicture* picture) {
-    SkBaseDevice* device = this->getTopDevice();
-    if (NULL != device) {
-        device->EXPERIMENTAL_purge(picture);
-    }
-}
-
 void SkCanvas::drawPicture(const SkPicture* picture) {
     if (NULL != picture) {
         this->onDrawPicture(picture);
     }
 }
 
 void SkCanvas::onDrawPicture(const SkPicture* picture) {
     SkASSERT(NULL != picture);
 
     SkBaseDevice* device = this->getTopDevice();
@@ skipping 96 matching lines @@
     if (!supported_for_raster_canvas(info)) {
         return NULL;
     }
 
     SkBitmap bitmap;
     if (!bitmap.installPixels(info, pixels, rowBytes)) {
         return NULL;
     }
     return SkNEW_ARGS(SkCanvas, (bitmap));
 }