Prefix build variables used in separate repos with mojo_

mojo/public/tools/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.gni")
 
-if (use_prebuilt_mojo_shell) {
+if (mojo_use_prebuilt_mojo_shell) {
   copy("copy_mojo_shell") {
     filename = "mojo_shell"
     if (is_android) {
       filename = "MojoShell.apk"
       sources = [
         "prebuilt/shell/android-arm/$filename",
       ]
       outputs = [
         "$root_out_dir/apks/$filename",
       ]
     } else {
       assert(is_linux)
       sources = [
         "prebuilt/shell/linux-x64/$filename",
       ]
       outputs = [
         "$root_out_dir/$filename",
       ]
     }
   }
 }
 
-if (use_prebuilt_network_service) {
+if (mojo_use_prebuilt_network_service) {
   copy("copy_network_service") {
     filename = "network_service.mojo"
-    if (defined(prebuilt_network_service_location) &&
-        prebuilt_network_service_location != "") {
+    if (defined(mojo_prebuilt_network_service_location) &&
+        mojo_prebuilt_network_service_location != "") {
       sources = [
-        "$prebuilt_network_service_location",
+        "$mojo_prebuilt_network_service_location",
       ]
     } else {
       if (is_android) {
         assert(cpu_arch == "arm",
                "Only arm version prebuilt netowrk_service.mojo is available.")
         sources = [
           "prebuilt/network_service/android-arm/$filename",
         ]
       } else {
         assert(is_linux)
@@ skipping 23 matching lines @@
     outputs = [
       "$root_out_dir/$filename",
     ]
   }
 }
 
 # This rule can be seen as a sort of adapter. This takes a dart framework
 # loaded from Google Storage and then puts it in a rule which the
 # "dart_package" template in mojo/public/dart/rules.gni can introspect on,
 # accessing the 'label' and 'target_out_dir' variables.
-if (use_dart_apptest_framework) {
+if (mojo_use_dart_apptest_framework) {
   copy("dart_apptest_framework") {
     sources = [
       "prebuilt/frameworks/apptest.dartzip",
     ]
     outputs = [
       "$target_out_dir/dart_apptest_framework.dartzip",
     ]
   }
 }