Increase hard timeout of webkit_unit_tests.

The set of tests "webkit_unit_tests" run close to the timeout and
sometimes exceed it. This CL increase hard timeout of webkit_unit_tests
on Marshmallow 64 bit Tester.

Previous timeout: 960
New timeout: 1200

Bug: 847229
Change-Id: I595f9a13de3039078dbf80c5ab02a082ab169c10
Reviewed-on: https://chromium-review.googlesource.com/1075335
Reviewed-by: John Budorick <[email protected]>
Commit-Queue: Arthur Sonzogni <[email protected]>
Cr-Commit-Position: refs/heads/master@{#562476}
diff --git a/testing/buildbot/test_suite_exceptions.pyl b/testing/buildbot/test_suite_exceptions.pyl
index 2116e1c..c32666b 100644
--- a/testing/buildbot/test_suite_exceptions.pyl
+++ b/testing/buildbot/test_suite_exceptions.pyl
@@ -2880,6 +2880,12 @@
           'shards': 5,
         },
       },
+      'Marshmallow 64 bit Tester': {
+        # Increase timeout. See https://crbug.com/847229.
+        'swarming': {
+          'hard_timeout': 1200,
+        },
+      },
     },
   },
   'webview_instrumentation_test_apk': {