Make SkSHA1 and SkM5 use common SkDigestHash result type

gm/tests/outputs/compared-against-different-pixels-images/output-expected/json-summary.txt

Index: gm/tests/outputs/compared-against-different-pixels-images/output-expected/json-summary.txt
===================================================================
--- gm/tests/outputs/compared-against-different-pixels-images/output-expected/json-summary.txt	(revision 8685)
+++ gm/tests/outputs/compared-against-different-pixels-images/output-expected/json-summary.txt	(working copy)
@@ -2,10 +2,10 @@
    "actual-results" : {
       "failed" : {
          "565/selftest1" : {
-            "checksum" : 9512553915271796906
+            "checksum" : "aad886e262610384"

[epoger, 2013/04/18 17:02:49]

Note that checksums are now recorded in little-endian hex form.

9512553915271796906 base 10
= 0x84036162E286D8AA base 16
= "aad886e262610384" when you reverse the bytes.

          },
          "8888/selftest1" : {
-            "checksum" : 14022967492765711532
+            "checksum" : "ac7c2647a3969bc2"
          }
       },
       "failure-ignored" : null,
@@ -14,11 +14,11 @@
    },
    "expected-results" : {
       "565/selftest1" : {
-         "checksums" : [ 11071285354315388429 ],
+         "checksums" : [ "0d16f41e5f1ba599" ],
          "ignore-failure" : false
       },
       "8888/selftest1" : {
-         "checksums" : [ 16527650414256125612 ],
+         "checksums" : [ "acf692097c025ee5" ],
          "ignore-failure" : false
       }
    }