Mojo: Make MessagePipe::ConvertLocalToProxy() create the ChannelEndpoint.

Mojo: Make MessagePipe::ConvertLocalToProxy() create the ChannelEndpoint.

This will be needed to move the "paused message queue" into the
ChannelEndpoint, since transferring messages from the
LocalMessagePipeEndpoint needs to happen "atomically" with its
conversion to a ProxyMessagePipeEndpoint. (Before the MessagePipe lock
is released, the ProxyMessagePipeEndpoint needs to have a place to queue
messages, and any already-queued messages must be at the front of that
queue.)

R=darin@chromium.org

Committed: https://crrev.com/0d2f449cd9c3f6ac459a712e182d350c0ff1b210
Cr-Commit-Position: refs/heads/master@{#295822}

[darin (slow to review), 2014-09-19 21:15:00]

lgtm

[viettrungluu, 2014-09-19 22:00:27]

The CQ bit was checked by viettrungluu@chromium.org

[commit-bot: I haz the power, 2014-09-19 22:01:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/585093002/20001

[commit-bot: I haz the power, 2014-09-19 22:02:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/585093002/20001

[commit-bot: I haz the power, 2014-09-19 23:44:38]

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

[commit-bot: I haz the power, 2014-09-19 23:44:39]

Try jobs failed on following builders:
  mac_chromium_rel_swarming on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[viettrungluu, 2014-09-20 00:07:14]

Committed patchset #2 (id:20001) manually as 0d2f449 (presubmit successful).

[commit-bot: I haz the power, 2014-09-20 00:07:16]

Patchset 2 (id:??) landed as
https://crrev.com/0d2f449cd9c3f6ac459a712e182d350c0ff1b210
Cr-Commit-Position: refs/heads/master@{#295822}