Mojo C++ bindings: Simplify associated interface API.

mojo/public/cpp/bindings/lib/may_auto_lock.h

Index: mojo/public/cpp/bindings/lib/may_auto_lock.h
diff --git a/mojo/public/cpp/bindings/lib/may_auto_lock.h b/mojo/public/cpp/bindings/lib/may_auto_lock.h
index 09ee705d79a65ee3b0e9c340b8d14feb1f193d98..42bbfae5d64ef0e10c771c598b6db819e0932f53 100644
--- a/mojo/public/cpp/bindings/lib/may_auto_lock.h
+++ b/mojo/public/cpp/bindings/lib/may_auto_lock.h
@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#ifndef MOJO_PUBLIC_CPP_BINDINGS_LIB_MAY_AUTO_LOCK_H_
+#define MOJO_PUBLIC_CPP_BINDINGS_LIB_MAY_AUTO_LOCK_H_
+
 #include "base/macros.h"
 #include "base/synchronization/lock.h"
 
@@ -52,3 +55,5 @@ class MayAutoUnlock {
 
 }  // namespace internal
 }  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_MAY_AUTO_LOCK_H_