Revert 186925 since it breaks many of the builds on the bots (e.g.

Revert 186925 since it breaks many of the builds on the bots (e.g.
http://build.chromium.org/p/chromium.perf/builders/Win%20Builder/builds/45240/steps/compile/logs/stdio).

> PPAPI: Remove threading options; it's always on
> 
> This also re-enables thread checking for the host side resource and var trackers. Before, checking was disabled everywhere.
> 
> BUG=159240, 92909
> 
> 
> Review URL: https://chromiumcodereview.appspot.com/12378050

TBR=dmichael@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=186939

[aberent, 2013-03-08 11:10:16]

Committed patchset #1 manually as r186939.