Use ScopedTaskEnvironment instead of MessageLoop in /ppapi/proxy

MessageLoop will go away, eventually.

ScopedTaskEnvironment will per default start a ThreadPool, which should
be fine in most of the cases. If you belive your test needs to make sure
that no ThreadPool runs let me know and I will update the patch.

This CL was uploaded by git cl split.

Change-Id: Ida93c455e32bf058063b6bf48800b289c972823b
Auto-Submit: Carlos Caballero <>
Reviewed-by: Antoine Labour <>
Commit-Queue: Antoine Labour <>
Cr-Original-Commit-Position: refs/heads/master@{#667191}
Cr-Mirrored-Commit: 87cbd6e88422ea70e50167d7113d2229b89e1497
2 files changed