Revert 191420 "PPAPI: Remove threading options; it's always on"

> 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
> 
> 
> Committed: r186925
> Reverted: r186939 due to build errors
> 
> Committed: r187340
> 
> Committed: r187427
> Reverted: r187668 due to a failing check in Canary, which was fixed here: r187681
> 
> Committed: r189518
> Reverted: r189682, due to regression in Kraken (see crbug.com/222741)
> 
> Review URL: https://chromiumcodereview.appspot.com/12378050

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Review URL: https://codereview.chromium.org/13328006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@191441 0039d316-1c4b-4281-b951-d872f2087c98
33 files changed