[Media Router] Update comment in BUILD.gn

Adds a TODO to the issue to fix dependencies.

TBR=takumif@chromium.org

Change-Id: I7b75ae3d4925e3f99cc62335a353cabd8bd89c8f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1951488Reviewed-by: mark a. foltz <mfoltz@chromium.org>
Commit-Queue: mark a. foltz <mfoltz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#721774}

chrome/browser/media/router/BUILD.gn

@@ -71,12 +71,15 @@ static_library("router") {
   if (enable_extensions) {
     deps += [
       "discovery",
-      # We can't depend on //chrome/browser/ui due to introducing a cyclic dependency,
-      # so we have to depend on this directly to fix include resolution for
-      # browser.h, which is used in multiple extension-only files.
-      "//components/signin/public/base:signin_buildflags",
       "//components/mirroring/mojom:host",
       "//components/mirroring/mojom:service",
+
+      # We can't depend on //chrome/browser/ui due to introducing a cyclic
+      # dependency, so we have to depend on this directly to fix include
+      # resolution for browser.h, which is used in multiple extension-only
+      # files.
+      # TODO(crbug.com/1030821): Resolve circular dependencies
+      "//components/signin/public/base:signin_buildflags",
       "//components/translate/content/common",
       "//mojo/public/cpp/bindings",
       "//ui/base:buildflags",