Temporarily Incrase Mojo FYI timeouts

Even with properly set timeouts, mash_browser_tests timeout about half the time
on the Mojo FYI bot. I want to see if an increased timeout can get them
consistently passing.

TBR=sky@chromium.org
TEST=none

Bug: 678687
Change-Id: I1b86980f981a3c00e5caf1c4aaae9f4c6ad06d8f
Reviewed-on: https://chromium-review.googlesource.com/593851Reviewed-by: Jonathan Ross <jonross@chromium.org>
Commit-Queue: Jonathan Ross <jonross@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491106}

testing/buildbot/chromium.fyi.json

@@ -10738,7 +10738,7 @@
         ],
         "swarming": {
           "can_use_on_swarming_builders": true,
-          "hard_timeout": 900
+          "hard_timeout": 1800
         },
         "test": "mash_browser_tests"
       },