Additional fixes for prerender/instant + browsing history.

content/browser/tab_contents/tab_contents.h

Index: content/browser/tab_contents/tab_contents.h
diff --git a/content/browser/tab_contents/tab_contents.h b/content/browser/tab_contents/tab_contents.h
index 0a7403a2897691f27483ea3c82f1884c8d6eb55c..2957f3429fc952395365242556f18d3d082c60f8 100644
--- a/content/browser/tab_contents/tab_contents.h
+++ b/content/browser/tab_contents/tab_contents.h
@@ -626,9 +626,10 @@ class TabContents : public PageNavigator,
   // Sets the history for this tab_contents to |history_length| entries, and
   // moves the current page_id to the last entry in the list if it's valid.
   // This is mainly used when a prerendered page is swapped into the current
-  // tab.
-  void SetHistoryLengthAndClear(int history_length);
-
+  // tab. The method is virtual for testing.
+  virtual void SetHistoryLengthAndPrune(const SiteInstance* site_instance,
+                                        int merge_history_length,
+                                        int32 minimum_page_id);
 
   // Misc non-view stuff -------------------------------------------------------