Fix SkOneShotDiscardablePixelRef to return discardable segment.

src/core/SkResourceCache.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkChecksum.h"
 #include "SkMessageBus.h"
 #include "SkMipMap.h"
@@ skipping 69 matching lines @@
 
     // Ownership of the discardablememory is transfered to the pixelref
     SkOneShotDiscardablePixelRef(const SkImageInfo&, SkDiscardableMemory*, size_t rowBytes);
     ~SkOneShotDiscardablePixelRef();
 
 protected:
     bool onNewLockPixels(LockRec*) override;
     void onUnlockPixels() override;
     size_t getAllocatedSizeInBytes() const override;
 
+    SkDiscardableMemory* diagnostic_only_getDiscardable() const override { return fDM; }
+
 private:
     SkDiscardableMemory* fDM;
     size_t               fRB;
     bool                 fFirstTime;
 
     typedef SkPixelRef INHERITED;
 };
 
 SkOneShotDiscardablePixelRef::SkOneShotDiscardablePixelRef(const SkImageInfo& info,
                                              SkDiscardableMemory* dm,
@@ skipping 579 matching lines @@
         dump->setDiscardableMemoryBacking(dump_name.c_str(), *discardable);
     } else {
         dump->dumpNumericValue(dump_name.c_str(), "size", "bytes", rec.bytesUsed());
         dump->setMemoryBacking(dump_name.c_str(), "malloc", nullptr);
     }
 }
 
 void SkResourceCache::DumpMemoryStatistics(SkTraceMemoryDump* dump) {
     VisitAll(sk_trace_dump_visitor, dump);
 }