Enable openscreen compilation in Chromium

This change enables third_party/openscreen to be built as part of gn_all
so we can get coverage on linux bots which will help to ensure we aren't
breaking our Chromium compatibility while we are still pre-integration.
This doesn't cause anything to be linked into any shipping binaries.

Bug: 951615
Change-Id: I65a67054d9545865a51c5dc3cf8d1bb206fc8391
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1562751
Reviewed-by: Mirko Bonadei <mbonadei@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Brandon Tolsch <btolsch@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#659696}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 58d0fc5b2cc4b1b14d2a93057f97d19c680e5a75
diff --git a/absl/strings/BUILD.gn b/absl/strings/BUILD.gn
index 0768579..52f6413 100644
--- a/absl/strings/BUILD.gn
+++ b/absl/strings/BUILD.gn
@@ -13,6 +13,7 @@
 if (build_with_chromium) {
   visibility = [
     "//libassistant/*",
+    "//third_party/openscreen/*",
     "//third_party/webrtc/*",
     "//third_party/abseil-cpp/*",
     "//third_party/googletest:gtest",
diff --git a/absl/types/BUILD.gn b/absl/types/BUILD.gn
index a483f5e..91404f5 100644
--- a/absl/types/BUILD.gn
+++ b/absl/types/BUILD.gn
@@ -13,6 +13,7 @@
 if (build_with_chromium) {
   visibility = [
     "//libassistant/*",
+    "//third_party/openscreen/*",
     "//third_party/webrtc/*",
     "//third_party/abseil-cpp/*",
     "//third_party/googletest:gtest",