Convert Jetstream benchmark to WprGo.

BUG=chromium:730036

Change-Id: Ie31d6e2f0375655185b7fcd8a9809bc24969b861
Reviewed-on: https://chromium-review.googlesource.com/595982
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Ned Nguyen <nednguyen@google.com>
Cr-Commit-Position: refs/heads/master@{#491087}

tools/perf/page_sets/data/jetstream.json

 {
     "archives": {
         "http://browserbench.org/JetStream/": {
-            "DEFAULT": "jetstream_000.wpr"
+            "DEFAULT": "jetstream_000.wprgo"
         }
     },
     "description": "Describes the Web Page Replay archives for a story set. Don't edit by hand! Use record_wpr for updating.",

tools/perf/page_sets/data/jetstream_000.wpr.sha1

-1212f1ea3fc3e8e2f2a6694032e86fc036cad108
\ No newline at end of file