IndexedDB: Fix trivial cpplint.py errors

content/common/indexed_db/indexed_db_param_traits.h

Index: content/common/indexed_db/indexed_db_param_traits.h
diff --git a/content/common/indexed_db/indexed_db_param_traits.h b/content/common/indexed_db/indexed_db_param_traits.h
index 9d684a40d02b0e7572e96ee181cf3d1170dfa91f..c091c3a8e8938c82b7a918d1989de4d61daab15b 100644
--- a/content/common/indexed_db/indexed_db_param_traits.h
+++ b/content/common/indexed_db/indexed_db_param_traits.h
@@ -5,6 +5,8 @@
 #ifndef CONTENT_COMMON_INDEXED_DB_INDEXED_DB_PARAM_TRAITS_H_
 #define CONTENT_COMMON_INDEXED_DB_INDEXED_DB_PARAM_TRAITS_H_
 
+#include <string>
+
 #include "ipc/ipc_message.h"
 #include "ipc/ipc_param_traits.h"
 
@@ -40,6 +42,6 @@ struct ParamTraits<content::IndexedDBKeyPath> {
   static void Log(const param_type& p, std::string* l);
 };
 
-} // namespace IPC
+}  // namespace IPC
 
 #endif  // CONTENT_COMMON_INDEXED_DB_INDEXED_DB_PARAM_TRAITS_H_