Set 'keepalive' flag for ViolationReport requests

Bug: 695939
Change-Id: I4f3ad7e06d44db7534a8750f3a344ad27bb4f460
Reviewed-on: https://chromium-review.googlesource.com/569328
Reviewed-by: Takeshi Yoshino <tyoshino@chromium.org>
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#486618}
2 files changed