Avoid stale navigation requests without excessive page id knowledge in the renderer process.

content/common/view_messages.h

Index: content/common/view_messages.h
diff --git a/content/common/view_messages.h b/content/common/view_messages.h
index d917c694f416ab6cc58e9b3c42cc96383c82f3de..07550e65b1a3a5b12e2ca64f18144999c71bb101 100644
--- a/content/common/view_messages.h
+++ b/content/common/view_messages.h
@@ -556,18 +556,12 @@ IPC_MESSAGE_ROUTED2(ViewMsg_UpdateVSyncParameters,
                     base::TimeTicks /* timebase */,
                     base::TimeDelta /* interval */)
 
-// Sent to the RenderView when a new tab is swapped into an existing
-// tab and the histories need to be merged. The existing tab has a history of
-// |merged_history_length| which precedes the history of the new tab. All
-// page_ids >= |minimum_page_id| in the new tab are appended to the history.
-//
-// For example, suppose the history of page_ids in the new tab's RenderView
-// is [4 7 8]. This is merged into an existing tab with 3 history items, and
-// all pages in the new tab with page_id >= 7 are to be preserved.
-// The resulting page history is [-1 -1 -1 7 8].
-IPC_MESSAGE_ROUTED2(ViewMsg_SetHistoryLengthAndPrune,
-                    int, /* merge_history_length */
-                    int32 /* minimum_page_id */)
+// Sent when the history is altered outside of navigation. The history list was
+// reset to |history_length| length, and the offset was reset to be
+// |history_offset|.
+IPC_MESSAGE_ROUTED2(ViewMsg_SetHistoryOffsetAndLength,
+                    int /* history_offset */,
+                    int /* history_length */)
 
 // Tells the renderer to create a new view.
 // This message is slightly different, the view it takes (via