The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/36dea83857801e2aa5d4934fefc2472ab9cca00b

commit 36dea83857801e2aa5d4934fefc2472ab9cca00b
Author: btolsch <btolsch@chromium.org>
Date: Thu Jul 13 03:29:14 2017

Fix some gn check errors with media router targets

In particular, /c/b/m/r/discovery cannot be built by itself because of
the missing mojo generator dependency.  This is useful for minimizing
what needs to be built for testing, especially on Windows where building
is much slower.

Bug:  740319 
Change-Id: I1b6aee574afac121b07d20936ff1a4717712fa3e
Reviewed-on: https://chromium-review.googlesource.com/566997
Reviewed-by: Derek Cheng <imcheng@chromium.org>
Commit-Queue: Brandon Tolsch <btolsch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#486255}
[modify] https://crrev.com/36dea83857801e2aa5d4934fefc2472ab9cca00b/chrome/browser/media/router/BUILD.gn
[modify] https://crrev.com/36dea83857801e2aa5d4934fefc2472ab9cca00b/chrome/browser/media/router/discovery/BUILD.gn
[modify] https://crrev.com/36dea83857801e2aa5d4934fefc2472ab9cca00b/chrome/test/media_router/BUILD.gn

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e5b9e92db735bcb24ea5055c3ac54a56266746aa

commit e5b9e92db735bcb24ea5055c3ac54a56266746aa
Author: btolsch <btolsch@chromium.org>
Date: Wed Nov 08 23:47:16 2017

Fix remaining non-circular gn check errors in Media Router targets

The gn check errors that remain after this change are things like
/c/b/m/router files including /c/browser files, but /c/b/m/router
depending on /c/browser would be a circular dependency.  This is
mostly due to siblings of Media Router that don't have their own
target underneath /c/browser and go directly into /c/browser:browser.

Bug:  740319 
Change-Id: Iee4a9594356c1959c26ff88e154da62e3f418831
Reviewed-on: https://chromium-review.googlesource.com/758812
Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Brandon Tolsch <btolsch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515009}
[modify] https://crrev.com/e5b9e92db735bcb24ea5055c3ac54a56266746aa/chrome/browser/media/router/discovery/BUILD.gn
[modify] https://crrev.com/e5b9e92db735bcb24ea5055c3ac54a56266746aa/extensions/browser/api/cast_channel/BUILD.gn

The remaining gn check errors are the result of cyclical dependencies (e.g. //chrome/browser:browser depends on //chrome/browser/media/router:router which includes files from //chrome/browser:browser) and I don't think it's worthwhile (or maybe even possible) to try to undo those cycles.