Fix regression with back-button not working on prerendered and instant pages.

content/browser/tab_contents/tab_contents.cc

Index: content/browser/tab_contents/tab_contents.cc
diff --git a/content/browser/tab_contents/tab_contents.cc b/content/browser/tab_contents/tab_contents.cc
index 14a387a62d7298b7d325c9325819baf2291c3afb..d021a40dc819f59a84308961fac8597cf2a072ea 100644
--- a/content/browser/tab_contents/tab_contents.cc
+++ b/content/browser/tab_contents/tab_contents.cc
@@ -1801,6 +1801,13 @@ void TabContents::LoadStateChanged(const GURL& url,
     NotifyNavigationStateChanged(INVALIDATE_LOAD | INVALIDATE_TAB);
 }
 
+void TabContents::OffsetAndPruneHistory(int offset) {
+  RenderViewHost* rvh = render_view_host();
+  if (!rvh)
+    return;
+  rvh->Send(new ViewMsg_OffsetAndPruneHistory(rvh->routing_id(), offset));
+}
+
 void TabContents::WorkerCrashed() {
   if (delegate())
     delegate()->WorkerCrashed(this);