add more tests for discardable caches

src/lazy/SkDiscardableMemoryPool.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 SkDiscardableMemoryPool_DEFINED
 #define SkDiscardableMemoryPool_DEFINED
 
 #include "SkDiscardableMemory.h"
 #include "SkTInternalLList.h"
 #include "SkThread.h"
 
+class SkPoolDiscardableMemory;
+
 #ifdef SK_DEBUG
     #define LAZY_CACHE_STATS 1
 #elif !defined(LAZY_CACHE_STATS)
     #define LAZY_CACHE_STATS 0
 #endif
 
 /**
  *  This non-global pool can be used for unit tests to verify that the
  *  pool works.
  */
-class SkPoolDiscardableMemory;
 class SkDiscardableMemoryPool : public SkDiscardableMemory::Factory {
 public:
     /**
      *  Without mutex, will be not be thread safe.
      */
     SkDiscardableMemoryPool(size_t budget, SkBaseMutex* mutex = NULL);
-    ~SkDiscardableMemoryPool();
-    SkDiscardableMemory* create(size_t bytes) SK_OVERRIDE;
+    virtual ~SkDiscardableMemoryPool();
+
+    virtual SkDiscardableMemory* create(size_t bytes) SK_OVERRIDE;
+
     size_t getRAMUsed();
     void setRAMBudget(size_t budget);
+
     /** purges all unlocked DMs */
     void dumpPool();
-    friend class SkPoolDiscardableMemory;
+
     #if LAZY_CACHE_STATS
     int          fCacheHits;
     int          fCacheMisses;
     #endif  // LAZY_CACHE_STATS
 
 private:
     SkBaseMutex* fMutex;
     size_t       fBudget;
     size_t       fUsed;
     SkTInternalLList<SkPoolDiscardableMemory> fList;
+
     /** Function called to free memory if needed */
     void dumpDownTo(size_t budget);
     /** called by SkDiscardableMemoryPool upon destruction */
     void free(SkPoolDiscardableMemory* dm);
     /** called by SkDiscardableMemoryPool::lock() */
     bool lock(SkPoolDiscardableMemory* dm);
     /** called by SkDiscardableMemoryPool::unlock() */
     void unlock(SkPoolDiscardableMemory* dm);
+
+    friend class SkPoolDiscardableMemory;
+
     typedef SkDiscardableMemory::Factory INHERITED;
 };
 
 /**
  *  Returns (and creates if needed) a threadsafe global
  *  SkDiscardableMemoryPool.
  */
 SkDiscardableMemoryPool* SkGetGlobalDiscardableMemoryPool();
 
 #if !defined(SK_DEFAULT_GLOBAL_DISCARDABLE_MEMORY_POOL_SIZE)
 #define SK_DEFAULT_GLOBAL_DISCARDABLE_MEMORY_POOL_SIZE (128 * 1024 * 1024)
 #endif
 
 #endif  // SkDiscardableMemoryPool_DEFINED