Revert IPC SyncChannel to base::WaitableEvent waiting

Revert IPC SyncChannel to base::WaitableEvent waiting

The new Mojo sync waiting behavior is causing some shutdown
hangs on Mac and test flake on Windows. Reverting for now
until that's sorted out.

Note that this behavior was landed as part of a larger change
which does not need to be reverted entirely, hence this
partial revert.

BUG=620866, 620683
TBR=jam@chromium.org since it's just a revert

Committed: https://crrev.com/7b7e60fe742530a34e7480307ae4d58d2f61eafa
Cr-Commit-Position: refs/heads/master@{#400287}

[Ken Rockot(use gerrit already), 2016-06-16 21:41:50]

Description was changed from

==========
Revert IPC SyncChannel to base::WaitableEvent waiting

The new Mojo sync waiting behavior is causing some shutdown
hangs on Mac and test flake on Windows. Reverting for now
until that's sorted out.

Note that this behavior was landed as part of a larger change
which does not need to be reverted entirely, hence this
partial revert.

BUG=620866,620683
==========

to

==========
Revert IPC SyncChannel to base::WaitableEvent waiting

The new Mojo sync waiting behavior is causing some shutdown
hangs on Mac and test flake on Windows. Reverting for now
until that's sorted out.

Note that this behavior was landed as part of a larger change
which does not need to be reverted entirely, hence this
partial revert.

BUG=620866,620683
TBR=jam@chromium.org since it's just a revert
==========

[Ken Rockot(use gerrit already), 2016-06-16 21:42:17]

The CQ bit was checked by rockot@chromium.org

[commit-bot: I haz the power, 2016-06-16 21:43:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/2077653002/1

[commit-bot: I haz the power, 2016-06-16 23:15:34]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-06-16 23:18:07]

Description was changed from

==========
Revert IPC SyncChannel to base::WaitableEvent waiting

The new Mojo sync waiting behavior is causing some shutdown
hangs on Mac and test flake on Windows. Reverting for now
until that's sorted out.

Note that this behavior was landed as part of a larger change
which does not need to be reverted entirely, hence this
partial revert.

BUG=620866,620683
TBR=jam@chromium.org since it's just a revert
==========

to

==========
Revert IPC SyncChannel to base::WaitableEvent waiting

The new Mojo sync waiting behavior is causing some shutdown
hangs on Mac and test flake on Windows. Reverting for now
until that's sorted out.

Note that this behavior was landed as part of a larger change
which does not need to be reverted entirely, hence this
partial revert.

BUG=620866,620683
TBR=jam@chromium.org since it's just a revert

Committed: https://crrev.com/7b7e60fe742530a34e7480307ae4d58d2f61eafa
Cr-Commit-Position: refs/heads/master@{#400287}
==========

[commit-bot: I haz the power, 2016-06-16 23:18:08]

Patchset 1 (id:??) landed as
https://crrev.com/7b7e60fe742530a34e7480307ae4d58d2f61eafa
Cr-Commit-Position: refs/heads/master@{#400287}