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

content/browser/frame_host/navigation_entry_impl.h

Index: content/browser/frame_host/navigation_entry_impl.h
diff --git a/content/browser/frame_host/navigation_entry_impl.h b/content/browser/frame_host/navigation_entry_impl.h
index 04162896b4793be53730fc0817eeb24e33b95314..c0953af1a2f40ab70d7eb8b79124ba4a9abf78dd 100644
--- a/content/browser/frame_host/navigation_entry_impl.h
+++ b/content/browser/frame_host/navigation_entry_impl.h
@@ -184,6 +184,7 @@ class CONTENT_EXPORT NavigationEntryImpl
       const FrameNavigationEntry& frame_entry,
       bool is_same_document_history_load,
       bool is_history_navigation_in_new_child,
+      bool has_subtree_history_items,
       bool has_committed_real_load,
       bool intended_as_new_entry,
       int pending_offset_to_send,
@@ -227,6 +228,15 @@ class CONTENT_EXPORT NavigationEntryImpl
   // there is one in this NavigationEntry.
   FrameNavigationEntry* GetFrameEntry(FrameTreeNode* frame_tree_node) const;
 
+  // Returns whether the TreeNode associated with |frame_tree_node| has any
+  // children.  If not, the renderer process does not need to ask the browser
+  // when new subframes are created during a back/forward navigation.
+  // TODO(creis): Send a data structure with all unique names in the subtree,
+  // along with any corresponding same-process PageStates.  The renderer only
+  // needs to ask the browser process to handle the cross-process cases.
+  // See https://crbug.com/639842.
+  bool HasSubtreeHistoryItems(FrameTreeNode* frame_tree_node) const;
+
   // Removes any subframe FrameNavigationEntries that match the unique name of
   // |frame_tree_node|, and all of their children. There should be at most one,
   // since collisions are avoided but leave old FrameNavigationEntries in the