Reland "[Media Router] Remove obsolete flags/features."

This reverts commit bbaf93c3.

Reason for revert:

Fixed compilation errors missed by the bots.

Original change's description:
> Revert "[Media Router] Remove obsolete flags/features."
>
> This reverts commit a04d299b.
>
> Reason for revert: [sheriff] compile errors on multiple bots. https://bugs.chromium.org/p/chromium/issues/detail?id=1236311
>
> Original change's description:
> > [Media Router] Remove obsolete flags/features.
> >
> > Removes the following flags/features:
> > - load-media-router-component-extension
> > - cast-media-route-provider
> > - kCastToMeetingFromCastDialog
> > - kCastFeedbackDialog
> > - kDialMediaRouteProvider
> >
> > Bug: 1179785,1028753
> > Change-Id: I1d422d629eccc7ff612d0b9c915011183d65ca15
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3063781


> > Commit-Queue: mark a. foltz <mfoltz@chromium.org>
> > Auto-Submit: mark a. foltz <mfoltz@chromium.org>
> > Reviewed-by: Filip Gorski <fgorski@chromium.org>
> > Reviewed-by: Takumi Fujimoto <takumif@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#908260}
>
> Bug: 1179785,1028753
> Change-Id: I4634974f8c8d416beda5bd347d34c7929bb82937
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3068730
> Commit-Queue: Hayato Ito <hayato@chromium.org>
> Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Owners-Override: Hayato Ito <hayato@chromium.org>
> Auto-Submit: Hayato Ito <hayato@chromium.org>
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Cr-Commit-Position: refs/heads/master@{#908292}

Bug: 1179785,1028753
Change-Id: Ie9d3e9be979a52fce3a9d63305ea2d3fdfd2ee66
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3072863


Commit-Queue: mark a. foltz <mfoltz@chromium.org>
Reviewed-by: Filip Gorski <fgorski@chromium.org>
Cr-Commit-Position: refs/heads/master@{#908678}