Revert of cc: Implement shared worker contexts.

Revert of cc: Implement shared worker contexts. (patchset #9 id:160001 of https://codereview.chromium.org/1336733002/ )

Reason for revert:
Broke GPU rasterization on Mac OS; please see https://code.google.com/p/chromium/issues/detail?id=523411#c26 .

I'm really sorry -- I don't know how this got past the CQ.

Original issue's description:
> cc: Implement shared worker contexts.
>
> This moves the responsibility to call BindToCurrentThread/SetupLock out
> of cc::OutputSurface and to the maintainer of the (possibly) shared
> context.
>
> OutputSurface now needs to be destroyed on the same thread they
> were created. OutputSurface::DetachFromClient() can be used to
> destroy any resources that need to be destroyed on the thread
> that the OutputSurface has been bound to.
>
> BUG=523411
> CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
>
> Committed: https://crrev.com/a47ef41ea03d3a5b8965eb700b682ddf8a1f055a
> Cr-Commit-Position: refs/heads/master@{#349274}

TBR=danakj@chromium.org,piman@chromium.org,sievers@chromium.org,reveman@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=523411
Committed: https://crrev.com/d29c2783db449ea8c802423887fa4669abb453d5
Cr-Commit-Position: refs/heads/master@{#349313}

[Ken Russell (switch to Gerrit), 2015-09-17 01:41:03]

Created Revert of cc: Implement shared worker contexts.

[commit-bot: I haz the power, 2015-09-17 01:41:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1356463002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1356463002/1

[commit-bot: I haz the power, 2015-09-17 01:43:10]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-17 01:43:48]

Patchset 1 (id:??) landed as
https://crrev.com/d29c2783db449ea8c802423887fa4669abb453d5
Cr-Commit-Position: refs/heads/master@{#349313}