Added Doc for GetAllocator in SkResourceCache and SkBitmapCache

src/core/SkResourceCache.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 SkResourceCache_DEFINED
 #define SkResourceCache_DEFINED
 
@@ skipping 46 matching lines @@
         const uint32_t* as32SkipCount() const { return this->as32() + 1; }
     };
 
     struct Rec {
         typedef SkResourceCache::Key Key;
 
         Rec() : fLockCount(1) {}
         virtual ~Rec() {}
 
         uint32_t getHash() const { return this->getKey().hash(); }
-        
+
         virtual const Key& getKey() const = 0;
         virtual size_t bytesUsed() const = 0;
-        
+
         // for SkTDynamicHash::Traits
         static uint32_t Hash(const Key& key) { return key.hash(); }
         static const Key& GetKey(const Rec& rec) { return rec.getKey(); }
 
     private:
         Rec*    fNext;
         Rec*    fPrev;
         int32_t fLockCount;
         int32_t fPad;
-        
+
         friend class SkResourceCache;
     };
 
     typedef const Rec* ID;
 
     /**
      *  Returns a locked/pinned SkDiscardableMemory instance for the specified
      *  number of bytes, or NULL on failure.
      */
     typedef SkDiscardableMemory* (*DiscardableFactory)(size_t bytes);
 
     /*
      *  The following static methods are thread-safe wrappers around a global
      *  instance of this cache.
      */
 
     static const Rec* FindAndLock(const Key& key);
     static const Rec* AddAndLock(Rec*);
     static void Add(Rec*);
     static void Unlock(ID);
 
     static size_t GetTotalBytesUsed();
     static size_t GetTotalByteLimit();
     static size_t SetTotalByteLimit(size_t newLimit);
 
     static size_t SetSingleAllocationByteLimit(size_t);
     static size_t GetSingleAllocationByteLimit();
 
+    /**
+     * Use this allocator for bitmaps, so they can use ashmem when available.
+     * Returns NULL if the ResourceCache has not been initialized with a DiscardableFactory.
+     */
     static SkBitmap::Allocator* GetAllocator();
 
     /**
      *  Call SkDebugf() with diagnostic information about the state of the cache
      */
     static void Dump();
 
     ///////////////////////////////////////////////////////////////////////////
 
     /**
@@ skipping 76 matching lines @@
 
     void init();    // called by constructors
 
 #ifdef SK_DEBUG
     void validate() const;
 #else
     void validate() const {}
 #endif
 };
 #endif