rename SkBitmapChecksummer as SkBitmapHasher, and prepare for it to possibly use

src/utils/SkBitmapChecksummer.h

Index: src/utils/SkBitmapChecksummer.h
===================================================================
--- src/utils/SkBitmapChecksummer.h	(revision 8638)
+++ src/utils/SkBitmapChecksummer.h	(working copy)
@@ -1,37 +0,0 @@
-
-/*
- * 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 SkBitmapChecksummer_DEFINED
-#define SkBitmapChecksummer_DEFINED
-
-#include "SkBitmap.h"
-#include "SkBitmapTransformer.h"
-
-/**
- * Static class that can generate checksums from SkBitmaps.
- */
-class SkBitmapChecksummer {
-public:
-    /**
-     * Returns a 64-bit checksum of the pixels in this bitmap.
-     *
-     * If this is unable to compute the checksum for some reason,
-     * it returns 0.
-     *
-     * 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 uint64_t Compute64(const SkBitmap& bitmap);
-
-private:
-    static uint64_t Compute64Internal(const SkBitmap& bitmap,
-                                      const SkBitmapTransformer& transformer);
-};
-
-#endif