Expose ability to download network service impl in SDK.

mojo/BUILD.gn

Index: mojo/BUILD.gn
diff --git a/mojo/BUILD.gn b/mojo/BUILD.gn
index 27541b950c58c0f1758962a1b153fb55e261ed80..4778a9af159ed84e0c6a5cd520e3ee445c433b5a 100644
--- a/mojo/BUILD.gn
+++ b/mojo/BUILD.gn
@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 import("//build/config/ui.gni")
+import("//build/module_args/mojo.gni")
 import("//mojo/public/mojo.gni")
 
 # TODO(beng): this meta target should probably move to the root dir's BUILD.gn.
@@ -67,6 +68,10 @@ group("tests") {
     "//services/window_manager:window_manager_unittests",
   ]
 
+  if (use_prebuilt_network_service) {
+    deps += [ "//mojo/public/tools:copy_network_service_apptests" ]
+  }
+
   if (!is_asan) {
     deps += [
       "//mojo/dart/embedder/test:dart_unittests",