Create a NavigationEntry for the initial blank page.

content/browser/frame_host/navigation_controller_impl.h

Index: content/browser/frame_host/navigation_controller_impl.h
diff --git a/content/browser/frame_host/navigation_controller_impl.h b/content/browser/frame_host/navigation_controller_impl.h
index a5136d932bd05c2d43f79c316699c4e17e8e459b..50926c54b913bcfe162fc88e4e4b3b19b073974c 100644
--- a/content/browser/frame_host/navigation_controller_impl.h
+++ b/content/browser/frame_host/navigation_controller_impl.h
@@ -79,6 +79,7 @@ class CONTENT_EXPORT NavigationControllerImpl
   void CancelPendingReload() override;
   void ContinuePendingReload() override;
   bool IsInitialNavigation() const override;
+  bool IsInitialBlankNavigation() const override;
   void Reload(bool check_for_repost) override;
   void ReloadIgnoringCache(bool check_for_repost) override;
   void ReloadOriginalRequestURL(bool check_for_repost) override;
@@ -90,6 +91,10 @@ class CONTENT_EXPORT NavigationControllerImpl
   void PruneAllButLastCommitted() override;
   void ClearAllScreenshots() override;
 
+  // This initializes the NavigationController with a NavigationEntry for the
+  // initial about:blank page, in the given SiteInstance.
+  void Init(SiteInstance* instance);
+
   // Whether this is the initial navigation in an unmodified new tab.  In this
   // case, we know there is no content displayed in the page.
   bool IsUnmodifiedBlankTab() const;