Before we just disable it, I'd like to understand why it doesn't work in the first place.  Devlin, is there a reason why our component extension isn't loaded by default in Guest mode?

Well let's try and fix the usability issue in M62 and then re-enable it later if we can resolve the underlying problem.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/548773c650f4e9fd8ddb70d05c657af76b283c34

commit 548773c650f4e9fd8ddb70d05c657af76b283c34
Author: mark a. foltz <mfoltz@chromium.org>
Date: Tue Aug 22 18:41:58 2017

[Media Router] Disable Media Router in guest sessions.

In guest sessions/profiles, the Media Router component extension is not
loaded.  Disable the entire feature in these sessions until the loading
problem is resolved.

Bug:  756243 
Change-Id: I300c79d95a10acb75ff4d80245a0effc15f10b0e
Reviewed-on: https://chromium-review.googlesource.com/624756
Commit-Queue: mark a. foltz <mfoltz@chromium.org>
Reviewed-by: Takumi Fujimoto <takumif@chromium.org>
Cr-Commit-Position: refs/heads/master@{#496383}
[modify] https://crrev.com/548773c650f4e9fd8ddb70d05c657af76b283c34/chrome/browser/media/router/media_router_feature.cc

There doesn't seem to be any Cast option present in the latest canary(62.0.3194.0) on Windows-10, Mac OS 10.12.5 and Linux Ubuntu 14.04.  Issue 758080  seems to be WAI.

Adding the verified label for this.

 Issue 758080  has been merged into this issue.