Tell renderer which subframes have history items on back/forward.

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 9523dbc4a089b87782057af8c1834e5cafadc8e2..52972d30c6c9bd1a67396d8d56f5bb348e8a0810 100644
--- a/content/renderer/render_frame_impl.h
+++ b/content/renderer/render_frame_impl.h
@@ -1096,16 +1096,16 @@ 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_;
+  // Keeps track of which future subframes the browser process has history items
+  // for during a history navigation.  The renderer process should ask the
+  // browser for history items when subframes with these names are created, and
+  // directly load the initial URLs for any other subframes.  This state is
+  // incrementally cleared as it is used and then reset in didStopLoading, since
+  // it is not needed after the first load completes and is never used after the
+  // initial navigation.
+  // TODO(creis): Expand this to include any corresponding same-process
+  // PageStates for the whole subtree in https://crbug.com/639842.
+  std::set<std::string> history_subframe_unique_names_;
 
   // Stores the current history item for this frame, so that updates to it can
   // be reported to the browser process via SendUpdateState.