Fix race on mojo message pump shutdown.

base/message_loop/message_loop.cc

Index: base/message_loop/message_loop.cc
diff --git a/base/message_loop/message_loop.cc b/base/message_loop/message_loop.cc
index 13bc854b038c5990cbc94f7ca07a94435717a65a..e84765a0f7a7e022764ce0db1509f572745c51a0 100644
--- a/base/message_loop/message_loop.cc
+++ b/base/message_loop/message_loop.cc
@@ -304,12 +304,7 @@ void MessageLoop::QuitWhenIdle() {
   if (run_loop_) {
     run_loop_->quit_when_idle_received_ = true;
   } else {
-    // We don't assert that run_loop_ is valid for custom message pumps. Some,
-    // for example MojoMessagePump, might have shutdown already based on other
-    // shutdown signals.
-    if (type_ != MessageLoop::TYPE_CUSTOM) {
-      NOTREACHED() << "Must be inside Run to call Quit";
-    }
+    NOTREACHED() << "Must be inside Run to call Quit";
   }
 }