Ensure that CopyStateFromAndPrune doesn't exceed kMaxSessionHistoryEntries.

content/browser/tab_contents/navigation_controller_impl.h

Index: content/browser/tab_contents/navigation_controller_impl.h
diff --git a/content/browser/tab_contents/navigation_controller_impl.h b/content/browser/tab_contents/navigation_controller_impl.h
index a261ecc68d69b5aada9dfaed26aaf5b44ef7b2a4..f79bf0a3bfca0ec4a2be82bb5556cc7e6c892a1a 100644
--- a/content/browser/tab_contents/navigation_controller_impl.h
+++ b/content/browser/tab_contents/navigation_controller_impl.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -248,6 +248,10 @@ class CONTENT_EXPORT NavigationControllerImpl
   // Discards the transient entry.
   void DiscardTransientEntry();
 
+  // If we have the maximum number of entries, remove the first one in
+  // preparation to add another.
+  void PruneFirstEntryIfFull();
+
   // Returns true if the navigation is redirect.
   bool IsRedirect(const ViewHostMsg_FrameNavigate_Params& params);