Prepare chrome to use the new Mojo EDK by default.

mojo/message_pump/handle_watcher.cc

Index: mojo/message_pump/handle_watcher.cc
diff --git a/mojo/message_pump/handle_watcher.cc b/mojo/message_pump/handle_watcher.cc
index dc3b9b9f37a8990600e0540acf941dfb9ca01eb8..73c423e45e17db07d7e7d7cdc271d8fc740ffd46 100644
--- a/mojo/message_pump/handle_watcher.cc
+++ b/mojo/message_pump/handle_watcher.cc
@@ -271,6 +271,12 @@ void WatcherThreadManager::AddRequest(const RequestData& data) {
     if (!was_empty)
       return;
   }
+
+  // With the new Mojo EDK, the MojoMessagePump will destruct when it sees that
+  // the IO thread has gone away. So at shutdown this can be null.
+  if (!thread_.task_runner())
+    return;
+
   // We outlive |thread_|, so it's safe to use Unretained() here.
   thread_.task_runner()->PostTask(
       FROM_HERE,