Migrate WebThreadSupportingGC from using CrossThreadBind

... in favor of CrossThreadBindOnce.

Reasoning: this method schedules a task that runs once.
Hence, coneptually CrossThreadBindOnce is the bind helper to be used.

BUG=963574
R=haraken@chromium.org, hiroshige@chromium.org

Change-Id: I0c1eede1ecbffeea3a14bacbd81fff40ce702712
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1619826
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Commit-Queue: Kentaro Hara <haraken@chromium.org>
Auto-Submit: Antonio Gomes <tonikitoo@igalia.com>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661357}
13 files changed