mojo: Use TYPE_DEFAULT message-loop for browser-tests.

services/shell/public/cpp/service_runner.h

Index: services/shell/public/cpp/service_runner.h
diff --git a/services/shell/public/cpp/service_runner.h b/services/shell/public/cpp/service_runner.h
index 45b574405180b1abbe687158d62671c4defd78e8..3e6283125e0daaa2fd683e3332ed46ca50ccd6a5 100644
--- a/services/shell/public/cpp/service_runner.h
+++ b/services/shell/public/cpp/service_runner.h
@@ -61,8 +61,7 @@ class ServiceRunner {
  private:
   std::unique_ptr<Service> service_;
 
-  // MessageLoop type. TYPE_CUSTOM is default (MessagePumpMojo will be used as
-  // the underlying message pump).
+  // MessageLoop type. Default is TYPE_DEFAULT.
   base::MessageLoop::Type message_loop_type_;
   // Whether Run() has been called.
   bool has_run_;