private iterator to visit all resource cache entries

src/lazy/SkDiscardablePixelRef.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkDiscardablePixelRef_DEFINED
 #define SkDiscardablePixelRef_DEFINED
 
 #include "SkDiscardableMemory.h"
 #include "SkImageGeneratorPriv.h"
 #include "SkImageInfo.h"
 #include "SkPixelRef.h"
 
 /**
  *  A PixelRef backed by SkDiscardableMemory, with the ability to
  *  re-generate the pixels (via a SkImageGenerator) if the DM is
  *  purged.
  */
 class SkDiscardablePixelRef : public SkPixelRef {
 public:
     
+    SkDiscardableMemory* diagnostic_only_getDiscardable() const override {
+        return fDiscardableMemory;
+    }
 
 protected:
     ~SkDiscardablePixelRef();
 
     bool onNewLockPixels(LockRec*) override;
     void onUnlockPixels() override;
     bool onLockPixelsAreWritable() const override { return false; }
 
     SkData* onRefEncodedData() override {
         return fGenerator->refEncodedData();
@@ skipping 27 matching lines @@
         return fGenerator->getYUV8Planes(sizes, planes, rowBytes, colorSpace);
     }
 
     friend bool SkInstallDiscardablePixelRef(SkImageGenerator*, const SkIRect*, SkBitmap*,
                                              SkDiscardableMemory::Factory*);
 
     typedef SkPixelRef INHERITED;
 };
 
 #endif  // SkDiscardablePixelRef_DEFINED