Extensions Cleanup: Simplify how code for IPC::ParamTraits<Manifest::Location> is generated.

extensions/common/manifest_location_param_traits.h

Index: extensions/common/manifest_location_param_traits.h
diff --git a/extensions/common/manifest_location_param_traits.h b/extensions/common/manifest_location_param_traits.h
index 15f7dde941a46e86a48719fc9990bcbdf11b7066..c0e8d3d9a32f19df0d3dc5c4e6890fdf6ff363d5 100644
--- a/extensions/common/manifest_location_param_traits.h
+++ b/extensions/common/manifest_location_param_traits.h
@@ -2,8 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef EXTENSIONS_COMMON_MANIFEST_LOCATION_PARAM_TRAITS_H_
-#define EXTENSIONS_COMMON_MANIFEST_LOCATION_PARAM_TRAITS_H_
+// Multiply-included file, hence no include guard.
 
 #include "extensions/common/manifest.h"
 #include "ipc/ipc_message_macros.h"
@@ -12,5 +11,3 @@
 IPC_ENUM_TRAITS_MIN_MAX_VALUE(extensions::Manifest::Location,
                               extensions::Manifest::INVALID_LOCATION,
                               extensions::Manifest::NUM_LOCATIONS - 1)
-
-#endif  // EXTENSIONS_COMMON_MANIFEST_LOCATION_PARAM_TRAITS_H_