Use per-frame task runners instead of per-thread task runners at pepper module

This CL is based on Alexander's CL: https://chromium-review.googlesource.com/c/chromium/src/+/1367329

Bug: 870606
Change-Id: I2ca696efeb203d7cb48c9f33034163c2d9c6277d
Reviewed-on: https://chromium-review.googlesource.com/c/1379607
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Hajime Hoshi <hajimehoshi@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#620986}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 5959c54fa966daba96b8b41d8741e651f0945cb0
7 files changed