Prevent downstream media targets from appearing in upstream chromium builds.

This CL adds a gn arg enable_downstream_media_tests, which downstream consumers
of chromium can set to make these builds appear. This prevents building and
isolate generation [which fails] in upstream chromium builds that try to
build/isolate all targets.

Bug: 876915
Change-Id: Ic0f892680e889a5cd5d92b8853800a3c08926a9b
Reviewed-on: https://chromium-review.googlesource.com/1186102Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585357}

chrome/test/media_router/BUILD.gn

@@ -2,6 +2,14 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+declare_args() {
+  # Many of the targets defined in this file have dependencies that cannot be
+  # satisfied without additional downstream resources. Explicitly guard them
+  # them behind this flag so that we do not attempt to build or isolate targets
+  # in public chromium checkouts.
+  enable_downstream_media_tests = false
+}
+
 source_set("browser_tests") {
   testonly = true
   defines = [ "HAS_OUT_OF_PROC_TEST_RUNNER" ]
@@ -66,7 +74,8 @@ copy("browser_test_resources") {
 
 # Run separately from the Chromium waterfall with the external component
 # extension.  See README.md
-group("media_router_e2e_tests") {
+if (enable_downstream_media_tests) {
+  group("media_router_e2e_tests") {
     testonly = true
     data_deps = [
       ":browser_test_resources",
@@ -77,6 +86,7 @@ group("media_router_e2e_tests") {
       "$root_out_dir/mr_extension/",
       "internal/",
     ]
+  }
 }
 
 copy("e2e_test_resources") {
@@ -91,7 +101,8 @@ copy("e2e_test_resources") {
 }
 
 # Run separately.  TODO: Documentation on how to run
-group("swarming_tests") {
+if (enable_downstream_media_tests) {
+  group("swarming_tests") {
     testonly = true
     data_deps = [
       ":browser_test_resources",
@@ -101,6 +112,7 @@ group("swarming_tests") {
       "internal/",
       "$root_out_dir/mr_extension/",
     ]
+  }
 }
 
 source_set("test_support") {
@@ -129,7 +141,8 @@ source_set("test_support") {
   ]
 }
 
-group("media_router_perf_tests") {
+if (enable_downstream_media_tests) {
+  group("media_router_perf_tests") {
     testonly = true
     data = [
       "$root_out_dir/media_router/telemetry_extension/",
@@ -143,6 +156,7 @@ group("media_router_perf_tests") {
     data_deps = [
       ":telemetry_extension_resources",
     ]
+  }
 }
 
 copy("telemetry_extension_resources") {