GitLab

This CL makes the task runners for IPC messages freezable.
In the follow up CL, I will filter out some messages that should not be
frozen. ( https://bugs.chromium.org/p/chromium/issues/detail?id=970080 )

Change-Id: I444f8db6377f2524f2a4f7c876af78e901be865d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1627834
Commit-Queue: Yuzu Saijo <yuzus@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#665788}