Coverity: Fix pass by value error.

chrome/common/extensions/extension_permission_set.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/common/extensions/extension_permission_set.h"
 
 #include <algorithm>
 #include <string>
 
 #include "base/command_line.h"
@@ skipping 362 matching lines @@
 ExtensionPermissionsInfo* ExtensionPermissionsInfo::GetInstance() {
   return Singleton<ExtensionPermissionsInfo>::get();
 }
 
 ExtensionAPIPermission* ExtensionPermissionsInfo::GetByID(
     ExtensionAPIPermission::ID id) {
   IDMap::iterator i = id_map_.find(id);
   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;
 }
 
 ExtensionAPIPermissionSet ExtensionPermissionsInfo::GetAll() {
   ExtensionAPIPermissionSet permissions;
   for (IDMap::const_iterator i = id_map_.begin(); i != id_map_.end(); ++i)
     permissions.insert(i->second->id());
   return permissions;
 }
@@ skipping 568 matching lines @@
   ExtensionOAuth2Scopes current_scopes = scopes();
   ExtensionOAuth2Scopes new_scopes = permissions->scopes();
   ExtensionOAuth2Scopes delta_scopes;
   std::set_difference(new_scopes.begin(), new_scopes.end(),
                       current_scopes.begin(), current_scopes.end(),
                       std::inserter(delta_scopes, delta_scopes.begin()));
 
   // We have less privileges if there are additional scopes present.
   return !delta_scopes.empty();
 }