GM: add --writeChecksumBasedFilenames option

gm/gm_expectations.h

Index: gm/gm_expectations.h
===================================================================
--- gm/gm_expectations.h	(revision 9460)
+++ gm/gm_expectations.h	(working copy)
@@ -76,6 +76,16 @@
          */
         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;