[Webapp Refactor] Cleans up the ClientSession.EventHandler interface.

[Webapp Refactor] Cleans up the ClientSession.EventHandler interface.

This CL provides a cleaner way to report session state changes with the following:
1. Removes onError() callback on ClientSession Handler.  Instead, if an error
   is encountered before the session connects, onConnectionFailed() will be called,
   and similarly, onDisconnected() will be called for errors encountered after
   a session is connected.
2. Removes the sessionStateChanged event on clientSession, so session state
   are reported consistently through the ClientSession.EventHandler interface.

BUG=477522
Committed: https://crrev.com/79a9a66e3152beef0545632aa30315456f2ebe74
Cr-Commit-Position: refs/heads/master@{#326853}

[kelvinp, 2015-04-23 18:58:03]

kelvinp@chromium.org changed reviewers:
+ garykac@chromium.org, jamiewalch@chromium.org

[kelvinp, 2015-04-23 18:58:22]

PTAL

[Jamie, 2015-04-24 18:09:09]

lgtm

https://codereview.chromium.org/1093373005/diff/1/remoting/webapp/crd/js/clie...
File remoting/webapp/crd/js/client_session.js (right):

https://codereview.chromium.org/1093373005/diff/1/remoting/webapp/crd/js/clie...
remoting/webapp/crd/js/client_session.js:272: return;
This appears in both your CLs.

[kelvinp, 2015-04-24 18:21:56]

The CQ bit was checked by kelvinp@chromium.org

[commit-bot: I haz the power, 2015-04-24 18:22:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1093373005/1

[commit-bot: I haz the power, 2015-04-24 19:09:56]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-24 19:10:50]

Patchset 1 (id:??) landed as
https://crrev.com/79a9a66e3152beef0545632aa30315456f2ebe74
Cr-Commit-Position: refs/heads/master@{#326853}