Gardening: Mark http/tests/serviceworker/skip-waiting.html as flaky timeout.
Gardening: Mark http/tests/serviceworker/skip-waiting.html as flaky timeout.

See http://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=http%2Ftests%2Fserviceworker%2Fskip-waiting.html&testType=layout-tests

BUG=444199
TBR=haraken@chromium.org,xiang.long@intel.com
NOTRY=true

Review URL: https://codereview.chromium.org/820793002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@187572 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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