[Media Router] Add "Hide in menu/Show in toolbar" option to Cast toolbar icon

This CL adds a context menu option of "Hide in menu/Show in toolbar" to the
Cast/Media Router toolbar action to match the functionality of the context menus
for extension actions. This menu option will be disabled when the action is in
the ephemeral state (i.e. the "Always show icon" option is unchecked, and the
icon only shows when Cast is in use), since the position of the icon would not
persist in those cases.

BUG=671399

Review-Url: https://codereview.chromium.org/2721953002
Cr-Commit-Position: refs/heads/master@{#454634}
7 files changed