[Browser Tests] Added a missing dep.

Chromium change:

https://source.chromium.org/chromium/chromium/src/+/6ca084ba33123e1499d50c379cb2bf33e15da316

commit 6ca084ba33123e1499d50c379cb2bf33e15da316
Author: yoshiki iguchi <yoshiki@chromium.org>
Date:   Tue Mar 2 05:06:36 2021 +0000

    [Code health] Fix deps issue in //browser/media/router

    - Fix 3 errors (7->4) in //chrome/browser/media/router/discovery
    - Fix 119 errors (225->106) in //chrome/browser/media/router

    BUG=1158908

test/BUILD.gn

@@ -809,6 +809,7 @@ if (!is_android) {
       "//chrome/app:command_ids",
       "//chrome/browser:browser_process",
       "//chrome/browser:theme_properties",
+      "//chrome/browser/media/router:media_router_feature",
       "//chrome/browser/ui",
       "//chrome/browser/web_applications/components",
       "//chrome/test:test_support_ui",