Mojo: Enable RemoteMessagePipeTest on Windows.

mojo/system/dispatcher.cc

Index: mojo/system/dispatcher.cc
diff --git a/mojo/system/dispatcher.cc b/mojo/system/dispatcher.cc
index c22a73bab6404bd1fe670cf3b38bba308763ff9f..0e39d2c7c7fd8de6646eb497097edb8ccdd3990c 100644
--- a/mojo/system/dispatcher.cc
+++ b/mojo/system/dispatcher.cc
@@ -11,6 +11,16 @@
 namespace mojo {
 namespace system {
 
+namespace test {
+
+// TODO(vtl): Maybe this should be defined in a test-only file instead.
+DispatcherTransport DispatcherTryStartTransport(
+    Dispatcher* dispatcher) {
+  return Dispatcher::CoreImplAccess::TryStartTransport(dispatcher);
+}
+
+}  // namespace test
+
 // Dispatcher ------------------------------------------------------------------
 
 // static