Prefix build variables used in separate repos with mojo_

mojo/public/mojo.gni

Index: mojo/public/mojo.gni
diff --git a/mojo/public/mojo.gni b/mojo/public/mojo.gni
index b8676e6bceba230a7bc421ce0da31cc5407ca1ce..e99586232d22616fd651e985525f9f7e2a34f064 100644
--- a/mojo/public/mojo.gni
+++ b/mojo/public/mojo.gni
@@ -14,14 +14,15 @@ if (!defined(build_mojo_shell_from_source) || !build_mojo_shell_from_source) {
 # If using the prebuilt network service, gate its usage by the platforms for
 # which it is published.
 use_prebuilt_network_service = false
-if (!defined(build_network_service_from_source) ||
-    !build_network_service_from_source) {
+if (!defined(mojo_build_network_service_from_source) ||
+    !mojo_build_network_service_from_source) {
   use_prebuilt_network_service = is_linux || is_android
 }
 
 # Enable Dart apptest framework by default.
 use_dart_apptest_framework = true
-if (defined(disable_dart_apptest_framework) && disable_dart_apptest_framework) {
+if (defined(mojo_disable_dart_apptest_framework) &&
+    mojo_disable_dart_apptest_framework) {
   use_dart_apptest_framework = false
 }