Notify the renderer if a history navigation has no subframe items.

content/renderer/render_frame_impl.h

Index: content/renderer/render_frame_impl.h
diff --git a/content/renderer/render_frame_impl.h b/content/renderer/render_frame_impl.h
index 561eb56b8230936d6610f9341c9b6f2552a23938..7a21b8438b2d81acdae332f8918d952aa3760106 100644
--- a/content/renderer/render_frame_impl.h
+++ b/content/renderer/render_frame_impl.h
@@ -1095,6 +1095,17 @@ class CONTENT_EXPORT RenderFrameImpl
   // didCreateDataSource().
   std::unique_ptr<NavigationParams> pending_navigation_params_;
 
+  // Keeps track of whether the browser process has any history items that need
+  // to be used for subframes of this frame (in the case of a history
+  // navigation).  If not, the renderer can skip sending an IPC to the browser
+  // and directly load any initial URLs for children itself.  This state is
+  // cleared during didStopLoading, since it is not needed after the first load
+  // completes and is never used after the initial navigation.  It is inherited
+  // by subframes.
+  // TODO(creis): Switch this to a data structure of unique names and
+  // corresponding same-process PageStates in https://crbug.com/639842.
+  bool browser_has_subtree_history_items_;
+
   // Stores the current history item for this frame, so that updates to it can
   // be reported to the browser process via SendUpdateState.
   blink::WebHistoryItem current_history_item_;