mojo: Add a runloop utility in python

third_party/cython/rules.gni

Index: third_party/cython/rules.gni
diff --git a/third_party/cython/rules.gni b/third_party/cython/rules.gni
index fce3e4caf7c4d12997dd9bcc812486cc604c8b0e..252e9487077fb0aeac0c200ed0d171afa4aa08b7 100644
--- a/third_party/cython/rules.gni
+++ b/third_party/cython/rules.gni
@@ -72,6 +72,9 @@ template("python_binary_module") {
       datadeps = invoker.datadeps
     }
     sources = [ cython_output ]
+    if (defined(invoker.additional_sources)) {
+      sources += invoker.additional_sources
+    }
     configs += [ ":$config_name" ]
   }