GM: add --writeChecksumBasedFilenames option

gm/gm_expectations.h

Index: gm/gm_expectations.h
===================================================================
--- gm/gm_expectations.h	(revision 9681)
+++ gm/gm_expectations.h	(working copy)
@@ -76,12 +76,33 @@
          */
         Json::Value asJsonTypeValuePair() const;
 
+        /**
+         * Returns the hashtype, such as "bitmap-64bitMD5", as an SkString.
+         */
+        SkString getHashType() const;
+
+        /**
+         * Returns the hash digest value, such as "12345", as an SkString.
+         */
+        SkString getDigestValue() const;
+
     private:
         bool fIsValid; // always check this first--if it's false, other fields are meaningless
         uint64_t fHashDigest;
     };
 
     /**
+     * Encapsulates an SkBitmap and its GmResultDigest, guaranteed to keep them in sync.
+     */
+    class BitmapAndDigest {
+    public:
+        BitmapAndDigest(const SkBitmap &bitmap) : fBitmap(bitmap), fDigest(bitmap) {}
+
+        const SkBitmap fBitmap;
+        const GmResultDigest fDigest;
+    };
+
+    /**
      * Test expectations (allowed image results, etc.)
      */
     class Expectations {