Ideally we should not show this at all if the user only has one display.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7d86b5d7ab28a04e4ace3c80efa879613173fa07

commit 7d86b5d7ab28a04e4ace3c80efa879613173fa07
Author: Takumi Fujimoto <takumif@chromium.org>
Date: Thu Jun 28 06:25:27 2018

[Harmony Cast Dialog] Show desktop picker when "Cast" is clicked

Before this CL, selecting desktop in the sources menu immediately
brought up the desktop picker. After this CL, the user will have to
first choose desktop, then click on the "Cast" button to show the
desktop picker.

This CL also temporarily removes local files from the list of sources,
until the feature is implemented.

Screenshot of the sources menu:
https://drive.google.com/open?id=1XAyTz05w3ZZdFuQay8QE2QC8NvFgWdwu

Bug:  857167 
Change-Id: Id55fc8c020e667fb0a081be0d62effeb3684cf8f
Reviewed-on: https://chromium-review.googlesource.com/1117567
Commit-Queue: Takumi Fujimoto <takumif@chromium.org>
Reviewed-by: mark a. foltz <mfoltz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571040}
[modify] https://crrev.com/7d86b5d7ab28a04e4ace3c80efa879613173fa07/chrome/app/media_router_strings.grdp
[modify] https://crrev.com/7d86b5d7ab28a04e4ace3c80efa879613173fa07/chrome/browser/ui/views/media_router/cast_dialog_view.cc
[modify] https://crrev.com/7d86b5d7ab28a04e4ace3c80efa879613173fa07/chrome/browser/ui/views/media_router/cast_dialog_view.h
[modify] https://crrev.com/7d86b5d7ab28a04e4ace3c80efa879613173fa07/chrome/browser/ui/views/media_router/cast_dialog_view_unittest.cc