Revert of WebGL: Refactor active context management.

Revert of WebGL: Refactor active context management. (https://codereview.chromium.org/251373005/)

Reason for revert:
This is likely to be the cause of crashes observed in
http://build.chromium.org/p/chromium.gpu/builders/Mac%20Debug%20%28Intel%29/builds/34596

Original issue's description:
> WebGL: Refactor active context management.
> 
> This CL makes WebGL lost&retore code more succinct.
> 
> 1. Deactive a context in loseContextImpl(), instead of dispatchContextLostEvent().
> Because of
> a) Prevent inconsistent state. Currently, activeContext() vector can store a lost
> context due to this, so oldestContextIndex() needs to check if active context is
> lost. Now we don't need redundant lostContext check. In addition, it does not
> make sense that active context list can store a lost context.
> b) In the same sense, only maybeRestoreContext() actives a context like loseContextImpl()
> in this CL.
> 
> 2. Don't call activeContexts().remove() adhoc.
> Only deactiveContext() calls activeContexts().remove() like only activeContext()
> calls activeContexts().append().
> 
> 3. Change the logic of dispatchContextLostEvent().
> Currently, when m_contextLostMode != RealLostContext, a context is added to
> forcibly evicted list, in which the context will be restored when another
> context is destructed. However, we start the restore-timer when
> the context is lost due to AutoRecoverSyntheticLostContext also. It means
> AutoRecoverSyntheticLostContext can restore twice. So this CL changes a context
> to be added into forcibly evicted list only if SyntheticLostContext.
> 
> BUG=392274
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=177833

[ccameron, 2014-07-10 19:26:16]

Created Revert of WebGL: Refactor active context management.

[commit-bot: I haz the power, 2014-07-10 19:27:14]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ccameron@chromium.org/388573004/1

[commit-bot: I haz the power, 2014-07-10 19:27:15]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-07-10 19:27:16]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer or
a provisional committer, _not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[dshwang, 2014-07-10 19:55:59]

Thank you for reporting.
This CL is already reverted by kbr@, https://codereview.chromium.org/382893002