Add a NOTREACHED for same document load with no history item.

content/renderer/render_frame_impl.cc

 // Copyright 2013 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.
 
 #include "content/renderer/render_frame_impl.h"
 
 #include <map>
 #include <string>
 #include <utility>
 #include <vector>
@@ skipping 5520 matching lines @@
                         ? blink::WebFrameLoadType::InitialHistoryLoad
                         : blink::WebFrameLoadType::BackForward;
         should_load_request = true;
 
         if (history_load_type == blink::WebHistorySameDocumentLoad) {
           // If this is marked as a same document load but we haven't committed
           // anything, treat it as a new load.  The browser shouldn't let this
           // happen.
           if (current_history_item_.isNull()) {
             history_load_type = blink::WebHistoryDifferentDocumentLoad;
+            NOTREACHED();
           } else {
             // Additionally, if the |current_history_item_|'s document
             // sequence number doesn't match the one sent from the browser, it
             // is possible that this renderer has committed a different
             // document. In such case, don't use WebHistorySameDocumentLoad.
             if (current_history_item_.documentSequenceNumber() !=
                 item_for_history_navigation.documentSequenceNumber()) {
               history_load_type = blink::WebHistoryDifferentDocumentLoad;
             }
           }
@@ skipping 800 matching lines @@
   // event target. Potentially a Pepper plugin will receive the event.
   // In order to tell whether a plugin gets the last mouse event and which it
   // is, we set |pepper_last_mouse_event_target_| to null here. If a plugin gets
   // the event, it will notify us via DidReceiveMouseEvent() and set itself as
   // |pepper_last_mouse_event_target_|.
   pepper_last_mouse_event_target_ = nullptr;
 #endif
 }
 
 }  // namespace content