Candidate for a post-branch bugfix.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/61c2840f00243135c7f22504ba0d8147db68b856

commit 61c2840f00243135c7f22504ba0d8147db68b856
Author: Takumi Fujimoto <takumif@chromium.org>
Date: Tue Jul 24 20:30:07 2018

[Harmony Cast Dialog] Disable the stop button when clicked

Disable the "Stop" button after it's clicked, so that the user doesn't
click on it repeatedly. The button becomes enabled again when there is
a model update, or if the user clicks on a sink.

When the stop button is clicked for a sink, the sink enters DISCONNECTING
state for that dialog, until its route is removed.

Bug:  848975 
Change-Id: I0acde957053a445fce6bb24cdb54c5e30dd45587
Reviewed-on: https://chromium-review.googlesource.com/1123326
Commit-Queue: Takumi Fujimoto <takumif@chromium.org>
Reviewed-by: mark a. foltz <mfoltz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577665}
[modify] https://crrev.com/61c2840f00243135c7f22504ba0d8147db68b856/chrome/browser/ui/media_router/ui_media_sink.h
[modify] https://crrev.com/61c2840f00243135c7f22504ba0d8147db68b856/chrome/browser/ui/views/media_router/cast_dialog_sink_button.cc
[modify] https://crrev.com/61c2840f00243135c7f22504ba0d8147db68b856/chrome/browser/ui/views/media_router/cast_dialog_sink_button_unittest.cc
[modify] https://crrev.com/61c2840f00243135c7f22504ba0d8147db68b856/chrome/browser/ui/views/media_router/cast_dialog_view.cc
[modify] https://crrev.com/61c2840f00243135c7f22504ba0d8147db68b856/chrome/browser/ui/views/media_router/cast_dialog_view_unittest.cc
[modify] https://crrev.com/61c2840f00243135c7f22504ba0d8147db68b856/chrome/browser/ui/views/media_router/media_router_views_ui.cc
[modify] https://crrev.com/61c2840f00243135c7f22504ba0d8147db68b856/chrome/browser/ui/views/media_router/media_router_views_ui.h
[modify] https://crrev.com/61c2840f00243135c7f22504ba0d8147db68b856/chrome/browser/ui/views/media_router/media_router_views_ui_unittest.cc