Prefix build variables used in separate repos with mojo_

mojo/services/http_server/public/interfaces/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/module_args/mojo.gni")
 import("$mojo_sdk_root/mojo/public/tools/bindings/mojom.gni")
 
 mojom("interfaces") {
   sources = [
     "http_request.mojom",
     "http_response.mojom",
     "http_server.mojom",
     "http_server_factory.mojom",
   ]
 
   import_dirs = [ get_path_info("../../../", "abspath") ]
 
-  if (defined(network_service_root)) {
-    import_dirs += [ network_service_root ]
+  if (defined(mojo_network_service_root)) {
+    import_dirs += [ mojo_network_service_root ]
   } else {
-    network_service_root = "../../.."
+    mojo_network_service_root = "../../.."
   }
 
   deps = [
-    "$network_service_root/network/public/interfaces",
+    "$mojo_network_service_root/network/public/interfaces",
   ]
 }