Mark http/tests/misc/script-sync-slow-scripts-onerror.html as flaky.
Mark http/tests/misc/script-sync-slow-scripts-onerror.html as flaky.

BUG=555052
TBR=

Review URL: https://codereview.chromium.org/1434393002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#359398}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk