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

src/utils/SkBitmapHasher.h

Index: src/utils/SkBitmapHasher.h
===================================================================
--- src/utils/SkBitmapHasher.h	(revision 8614)
+++ src/utils/SkBitmapHasher.h	(working copy)
@@ -6,32 +6,37 @@
  * found in the LICENSE file.
  */
 
-#ifndef SkBitmapChecksummer_DEFINED
-#define SkBitmapChecksummer_DEFINED
+#ifndef SkBitmapHasher_DEFINED
+#define SkBitmapHasher_DEFINED
 
 #include "SkBitmap.h"
 #include "SkBitmapTransformer.h"
 
+// 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 checksums from SkBitmaps.
+ * Static class that can generate an SkHashDigest from an SkBitmap.
  */
-class SkBitmapChecksummer {
+class SkBitmapHasher {
 public:
     /**
-     * Returns a 64-bit checksum of the pixels in this bitmap.
+     * Fills in "result" with a hash of the pixels in this bitmap.
      *
-     * If this is unable to compute the checksum for some reason,
-     * it returns 0.
+     * 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 uint64_t Compute64(const SkBitmap& bitmap);
+    static bool ComputeDigest(const SkBitmap& bitmap, SkHashDigest *result);
 
 private:
-    static uint64_t Compute64Internal(const SkBitmap& bitmap,
-                                      const SkBitmapTransformer& transformer);
+    static bool ComputeDigestInternal(const SkBitmap& bitmap,
+                                      const SkBitmapTransformer& transformer,
+                                      SkHashDigest *result);
 };
 
 #endif