Remove WebContentsObserver::ProvisionalChangeToMainFrameUrl and all the code supporting it.

content/common/frame_messages.h

Index: content/common/frame_messages.h
diff --git a/content/common/frame_messages.h b/content/common/frame_messages.h
index 1bc23d20472c0e1a14af69ab1a4564eb7f435e1d..61a0f155386c72252bf0403f965959928f24c038 100644
--- a/content/common/frame_messages.h
+++ b/content/common/frame_messages.h
@@ -517,12 +517,6 @@ IPC_MESSAGE_ROUTED2(FrameHostMsg_DidStartProvisionalLoadForFrame,
 IPC_MESSAGE_ROUTED1(FrameHostMsg_DidFailProvisionalLoadWithError,
                     FrameHostMsg_DidFailProvisionalLoadWithError_Params)
 
-// Sent when a provisional load on the main frame redirects.
-IPC_MESSAGE_ROUTED3(FrameHostMsg_DidRedirectProvisionalLoad,
-                    int /* page_id */,
-                    GURL /* source_url*/,
-                    GURL /* target_url */)
-
 // Notifies the browser that a frame in the view has changed. This message
 // has a lot of parameters and is packed/unpacked by functions defined in
 // render_messages.h.