Add a "mode" tag to key in DM json output.

Add a "mode" tag to key in DM json output.

This lets us distinguish the original ("direct") runs from their replay modes.

There was a bit of a bug in here now fixed: we used the first entry in
fSuffixes as the config.  Actually, the last entry in suffixes is the
config.  This is moot when there's only one suffix (direct drawing), but
for mode drawing we were recording the mode as config!  Now it's correct.

Here's some example output where I rigged a bunch of modes to fail:

{
   "results" : [
      {
         "key" : {
            "config" : "565",
            "mode" : "default-nobbh",
            "name" : "xfermodes2"
         },
         "md5" : "2daf6f7e2b8e56543b92068a10d2179e",
         "options" : {
            "source_type" : "GM"
         }
      },
      {
         "key" : {
            "config" : "8888",
            "mode" : "default-nobbh",
            "name" : "xfermodes2"
         },
         "md5" : "490361e8a52800d29558bc23876da8c6",
         "options" : {
            "source_type" : "GM"
         }
      },
...
      {
         "key" : {
            "config" : "565",
            "mode" : "direct",
            "name" : "xfermodes2"
         },
         "md5" : "92a3801d5914d6c2662904a3bb50d2b9",
         "options" : {
            "source_type" : "GM"
         }
      },
...
      {
         "key" : {
            "config" : "8888",
            "mode" : "direct",
            "name" : "xfermodes2"
         },
         "md5" : "e7e8b3e9d31e601acaaff4633ed5f63a",
         "options" : {
            "source_type" : "GM"
         }
      },


BUG=skia:

Committed: https://skia.googlesource.com/skia/+/87e2437fe574a5ed76caa225c4ff6464641ef64f

[mtklein, 2014-09-19 17:21:07]

mtklein@google.com changed reviewers:
+ jcgregorio@google.com, mtklein@google.com

[mtklein, 2014-09-19 17:21:07]

Just noticed this while looking at Florin's failures.

[jcgregorio, 2014-09-19 17:26:26]

On 2014/09/19 17:21:07, mtklein wrote:
> Just noticed this while looking at Florin's failures.

LGTM

[mtklein, 2014-09-19 17:26:59]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2014-09-19 17:27:53]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/586533005/1

[commit-bot: I haz the power, 2014-09-19 17:35:11]

Committed patchset #1 (id:1) as 87e2437fe574a5ed76caa225c4ff6464641ef64f