Rename elapsed-time field in Chromoting log events to session-duration, to align with server-side f…

Rename elapsed-time field in Chromoting log events to session-duration, and record time in seconds, to align with server-side field names and units.

BUG=461610
Tested by running run_webapp_unittest.py with these changes; all tests passed.

Committed: https://crrev.com/bd907bb661972284eab39dd75fcf5dcd5eb54868
Cr-Commit-Position: refs/heads/master@{#319200}

[anandc, 2015-03-04 23:41:51]

Patchset #1 (id:1) has been deleted

[anandc, 2015-03-04 23:43:14]

anandc@chromium.org changed reviewers:
+ jamiewalch@chromium.org

[anandc, 2015-03-04 23:43:15]

Jamie, could you PTAL? Thank you.

[rmsousa, 2015-03-04 23:45:57]

rmsousa@chromium.org changed reviewers:
+ rmsousa@chromium.org

[rmsousa, 2015-03-04 23:45:57]

lgtm

[anandc, 2015-03-05 00:01:38]

The CQ bit was checked by anandc@chromium.org

[commit-bot: I haz the power, 2015-03-05 00:02:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/961053004/20001

[commit-bot: I haz the power, 2015-03-05 02:58:29]

Committed patchset #1 (id:20001)

[commit-bot: I haz the power, 2015-03-05 02:58:59]

Patchset 1 (id:??) landed as
https://crrev.com/bd907bb661972284eab39dd75fcf5dcd5eb54868
Cr-Commit-Position: refs/heads/master@{#319200}