Add Open Screen unit tests

This patch adds additional dependencies on Open Screen to enable running
unit tests inside of Chrome.

This adds a new openscreen_unittests target
and adds it to the builders.

The following TODO is also added:
TODO(crbug.com/1025244): Move Open Screen unit tests from fieldtrial
to linux, mac bots once we have ensured the tests are stable.

Change-Id: Ia36d5af5136cbf39d5c1582238a0e5a1f69b7ddc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1880544
Commit-Queue: Jordan Bayles <jophba@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Aaron Gable <agable@chromium.org>
Reviewed-by: mark a. foltz <mfoltz@chromium.org>
Reviewed-by: Yuri Wiitala <miu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#727180}

diff --git a/BUILD.gn b/BUILD.gn
index b309339..85f1b33 100644
--- a/BUILD.gn
+++ b/BUILD.gn

@@ -13,6 +13,7 @@
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/ui.gni")
 import("//build/util/generate_wrapper.gni")
+import("//chrome/browser/media/router/features.gni")
 import("//components/nacl/features.gni")
 import("//device/vr/buildflags/buildflags.gni")
 import("//extensions/buildflags/buildflags.gni")
@@ -211,6 +212,10 @@
     ]
   }
 
+  if (enable_openscreen) {
+    deps += [ "//chrome/browser/media/router:openscreen_unittests" ]
+  }
+
   if (!is_ios && !is_fuchsia) {
     deps += [
       "//chrome/test:telemetry_perf_unittests",