Move unique name generation and tracking into //content.

third_party/WebKit/Source/web/WebHistoryItem.cpp

Index: third_party/WebKit/Source/web/WebHistoryItem.cpp
diff --git a/third_party/WebKit/Source/web/WebHistoryItem.cpp b/third_party/WebKit/Source/web/WebHistoryItem.cpp
index 7dafe65c0362e9d925de5786ca54897371ee6d7f..d5ad7f7b4ff866ab93343bee8d58a460dd33d409 100644
--- a/third_party/WebKit/Source/web/WebHistoryItem.cpp
+++ b/third_party/WebKit/Source/web/WebHistoryItem.cpp
@@ -78,12 +78,12 @@ void WebHistoryItem::setReferrer(const WebString& referrer,
       Referrer(referrer, static_cast<ReferrerPolicy>(referrerPolicy)));
 }
 
-WebString WebHistoryItem::target() const {
-  return m_private->target();
+const WebString& WebHistoryItem::target() const {
+  return m_target;
 }
 
 void WebHistoryItem::setTarget(const WebString& target) {
-  m_private->setTarget(target);
+  m_target = target;
 }
 
 WebFloatPoint WebHistoryItem::visualViewportScrollOffset() const {