I believe we can also remove the media_router_extension_id() API as well.

Not just a layering violation, this code is plain wrong. In tests the dynamic type of router_ could be MockMediaRouter.

I'm moving extension-related code out of MediaRouterMojoImpl into a new class media_router::EventPageRequestManager here [1], so I can add something like EventPageRequestManager::kExtensionId.

[1] https://codereview.chromium.org/2949933002/

takumif@: how soon do you think you will be able to make that change? I have a quick fix for the MediaRouterUITest.SetsForcedCastModeWithPresentationURLs test to unblock  issue 727993  and I was wondering whether to bother with that or to wait for your change.

The fix will be simple once 2949933002 lands, so I should be able to fix it in a few days.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/bae32143ddf7c4cf69f0f71e260a194648e0b27b

commit bae32143ddf7c4cf69f0f71e260a194648e0b27b
Author: takumif <takumif@chromium.org>
Date: Mon Jul 10 23:24:07 2017

[Media Router] Remove the extension ID getter from MRMojoImpl

This CL removes the media_route_provider_extension_id() getter from
MediaRouterMojoImpl, which was previously being accessed by static-casting
MediaRouter into MediaRouterMojoImpl. The getter in EventPageRequestManager is
now used.

It seems that we cannot simply hard-code the ID, since it's different between
dev and release builds of the component extension.

BUG= 597778 
BUG= 727993 

Review-Url: https://codereview.chromium.org/2970273002
Cr-Commit-Position: refs/heads/master@{#485439}

[modify] https://crrev.com/bae32143ddf7c4cf69f0f71e260a194648e0b27b/chrome/browser/media/router/mojo/media_router_mojo_impl.cc
[modify] https://crrev.com/bae32143ddf7c4cf69f0f71e260a194648e0b27b/chrome/browser/media/router/mojo/media_router_mojo_impl.h
[modify] https://crrev.com/bae32143ddf7c4cf69f0f71e260a194648e0b27b/chrome/browser/ui/toolbar/media_router_contextual_menu.cc
[modify] https://crrev.com/bae32143ddf7c4cf69f0f71e260a194648e0b27b/chrome/browser/ui/webui/cast/cast_ui.cc
[modify] https://crrev.com/bae32143ddf7c4cf69f0f71e260a194648e0b27b/chrome/browser/ui/webui/media_router/media_router_ui.cc
[modify] https://crrev.com/bae32143ddf7c4cf69f0f71e260a194648e0b27b/chrome/browser/ui/webui/media_router/media_router_ui.h