Coverity: Fix pass by value error.

chrome/common/extensions/extension_permission_set.cc

Index: chrome/common/extensions/extension_permission_set.cc
diff --git a/chrome/common/extensions/extension_permission_set.cc b/chrome/common/extensions/extension_permission_set.cc
index cf2e40f802a4d89f8f1e46748cda540280f978c6..4b7e39e2519588c35c5f7c72502db16096a0a4b5 100644
--- a/chrome/common/extensions/extension_permission_set.cc
+++ b/chrome/common/extensions/extension_permission_set.cc
@@ -380,7 +380,8 @@ ExtensionAPIPermission* ExtensionPermissionsInfo::GetByID(
   return (i == id_map_.end()) ? NULL : i->second;
 }
 
-ExtensionAPIPermission* ExtensionPermissionsInfo::GetByName(std::string name) {
+ExtensionAPIPermission* ExtensionPermissionsInfo::GetByName(
+    const std::string& name) {
   NameMap::iterator i = name_map_.find(name);
   return (i == name_map_.end()) ? NULL : i->second;
 }