Cleanup: Pass std::string as const reference from content/

content/renderer/history_entry.cc

Index: content/renderer/history_entry.cc
diff --git a/content/renderer/history_entry.cc b/content/renderer/history_entry.cc
index 24d6aea412fd68088379da83f235a1d24513adfb..8a2d20de95bab7d222c077ba70c017a508ee583c 100644
--- a/content/renderer/history_entry.cc
+++ b/content/renderer/history_entry.cc
@@ -117,7 +117,7 @@ HistoryEntry::HistoryNode::~HistoryNode() {
   if (!entry_ || item_.isNull())
     return;
 
-  for (std::string name : unique_names_) {
+  for (const std::string& name : unique_names_) {
     if (entry_->unique_names_to_items_[name] == this)
       entry_->unique_names_to_items_.erase(name);
   }