Switch HistoryTabHelper to use WebContentsUserData.

BUG=107201
TEST=no visible change


Review URL: https://chromiumcodereview.appspot.com/10993073

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@159278 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/chrome/browser/prerender/prerender_contents.cc b/chrome/browser/prerender/prerender_contents.cc
index 9ff1758..d1dd2500 100644
--- a/chrome/browser/prerender/prerender_contents.cc
+++ b/chrome/browser/prerender/prerender_contents.cc
@@ -684,8 +684,10 @@
 }
 
 void PrerenderContents::CommitHistory(TabContents* tab) {
+  HistoryTabHelper* history_tab_helper =
+    HistoryTabHelper::FromWebContents(tab->web_contents());
   for (size_t i = 0; i < add_page_vector_.size(); ++i)
-    tab->history_tab_helper()->UpdateHistoryForNavigation(add_page_vector_[i]);
+    history_tab_helper->UpdateHistoryForNavigation(add_page_vector_[i]);
 }
 
 Value* PrerenderContents::GetAsValue() const {