[Media Router WebUI] Move replace route responsibility to extension

[Media Router WebUI] Move replace route responsibility to extension

Currently the MR dialog controls the replace route functionality by
stopping the current route and starting a new one when that completes.
This doesn't allow the extension to optimize the change of source. This
change replaces the current UI behavior by simply calling CreateRoute
with the same sink and new source. This requires an extension change to
support accepting CreateRoute calls to a sink with an existing route.

BUG=614144
NOTRY=true
NOPRESUBMIT=true

Review-Url: https://codereview.chromium.org/2142613002
Cr-Commit-Position: refs/heads/master@{#410607}
(cherry picked from commit bbc838f3a5ed945462a29818591753e2cdb04f5c)

[btolsch, 2016-08-11 04:05:50]

btolsch@chromium.org changed reviewers:
+ imcheng@chromium.org

[btolsch, 2016-08-11 04:05:51]

Merging to M53, no conflicts.  PTAL, thanks!

[imcheng, 2016-08-11 04:14:08]

lgtm

[btolsch, 2016-08-11 04:14:34]

The CQ bit was checked by btolsch@chromium.org

[commit-bot: I haz the power, 2016-08-11 04:14:54]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-08-11 04:17:01]

Committed patchset #1 (id:1)