Mojo: Factor Channel::EndpointInfo out to ChannelEndpoint.

Mojo: Factor Channel::EndpointInfo out to ChannelEndpoint.

Also do a bunch of other small things. See the plan at the top of
channel_endpoint.h.

R=darin@chromium.org

Committed: https://crrev.com/633614a67da058685dda839771a887c54f987a62
Cr-Commit-Position: refs/heads/master@{#293444}

[darin (slow to review), 2014-09-04 23:40:03]

LGTM

[viettrungluu, 2014-09-05 00:17:02]

The CQ bit was checked by viettrungluu@chromium.org

[commit-bot: I haz the power, 2014-09-05 00:21:33]

CQ is trying da patch. Follow status at

https://chromium-status.appspot.com/cq/viettrungluu@chromium.org/541233002/20001

[commit-bot: I haz the power, 2014-09-05 05:00:20]

Committed patchset #2 (id:20001) as 596337174cd651d3efe1b2353f1ecaebd76bba8e

[commit-bot: I haz the power, 2014-09-10 03:37:00]

Patchset 2 (id:??) landed as
https://crrev.com/633614a67da058685dda839771a887c54f987a62
Cr-Commit-Position: refs/heads/master@{#293444}