[Media Router WebUI] Remove flex layout from cast button

[Media Router WebUI] Remove flex layout from cast button

The cast button in the route details view should not fill the remaining
horizontal space it has, so this change removes the flex property from
it.

BUG=618508
NOTRY=true
NOPRESUBMIT=true

Review-Url: https://codereview.chromium.org/2049953003
Cr-Commit-Position: refs/heads/master@{#399003}
(cherry picked from commit b4a9571b30800a635327ab6fe40eb8014901f8e0)

[btolsch, 2016-06-13 18:22:21]

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

[btolsch, 2016-06-13 18:22:22]

Merging to M52, no conflicts. PTAL, thanks!

[apacible, 2016-06-13 18:27:52]

rs lgtm

[btolsch, 2016-06-13 18:39:55]

The CQ bit was checked by btolsch@chromium.org

[commit-bot: I haz the power, 2016-06-13 18:40:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/2059353002/1

[commit-bot: I haz the power, 2016-06-13 18:43:20]

Committed patchset #1 (id:1)