[media_perftests] Disable retries.

This prevents the waterfall from retrying failures of media_perftests.

Bug: 785554
Change-Id: I5d2e044a6749c938bae1bfbf567717971623cb77
Reviewed-on: https://chromium-review.googlesource.com/773464
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Fredrik Hubinette <hubbe@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517533}

testing/buildbot/gn_isolate_map.pyl

@@ -1030,6 +1030,7 @@
     "args": [
       "media_perftests",
       "--single-process-tests",
+      "--test-launcher-retry-limit=0",
     ],
   },
   "load_library_perf_tests": {