SkBitmapHasher: use 64-bit-truncated MD5 instead of 64-bit CityHash

src/utils/SkBitmapHasher.h

 
 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkBitmapHasher_DEFINED
 #define SkBitmapHasher_DEFINED
 
 #include "SkBitmap.h"
 
+#define BITMAPHASHER_USES_TRUNCATED_MD5
+
 // TODO(epoger): Soon, SkHashDigest will become a real class of its own,
 // and callers won't be able to assume it converts to/from a uint64_t.
 typedef uint64_t SkHashDigest;
 
 /**
  * Static class that can generate an SkHashDigest from an SkBitmap.
  */
 class SkBitmapHasher {
 public:
     /**
      * Fills in "result" with a hash of the pixels in this bitmap.
      *
      * If this is unable to compute the hash for some reason,
      * it returns false.
      *
      * Note: depending on the bitmap config, we may need to create an
      * intermediate SkBitmap and copy the pixels over to it... so in some
      * cases, performance and memory usage can suffer.
      */
     static bool ComputeDigest(const SkBitmap& bitmap, SkHashDigest *result);
 
 private:
     static bool ComputeDigestInternal(const SkBitmap& bitmap, SkHashDigest *result);
 };
 
 #endif