[scheduler] Speculative fix for crbug.com/813218

Bug 813218 sounds like we fail to schedule PumpThrottledTasks and
throttling machinery grinds to a halt. Reduce the probability of this
by ensuring that a call to PumpThrottledTasks is always scheduled.

R=skyostil@chromium.org
TBR=altimin@chromium.org
BUG=813218

(cherry picked from commit 5a8814f02d665603fea6dc6372005eef196275f6)

Change-Id: Ie963d1eae456e39266bc8b347fdae0fa2bd37e7e
Reviewed-on: https://chromium-review.googlesource.com/946588
Commit-Queue: Alexander Timin <altimin@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#540642}
Reviewed-on: https://chromium-review.googlesource.com/948902
Reviewed-by: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/branch-heads/3325@{#656}
Cr-Branched-From: bc084a8b5afa3744a74927344e304c02ae54189f-refs/heads/master@{#530369}
1 file changed