PlzNavigate: make content unit tests work with browser side navigation

content/browser/frame_host/navigator.h

Index: content/browser/frame_host/navigator.h
diff --git a/content/browser/frame_host/navigator.h b/content/browser/frame_host/navigator.h
index d39293c22f074367414a9e42e32bed3c9ac4fb1c..191a58366227634b7e51db019cc8cdf6f5453019 100644
--- a/content/browser/frame_host/navigator.h
+++ b/content/browser/frame_host/navigator.h
@@ -149,6 +149,11 @@ class CONTENT_EXPORT Navigator : public base::RefCounted<Navigator> {
       const base::TimeTicks& renderer_before_unload_start_time,
       const base::TimeTicks& renderer_before_unload_end_time) {}
 
+  // PlzNavigate
+  // Returns whether there is an ongoing navigation waiting for the BeforeUnload
+  // event to execute in the renderer process.
+  virtual bool IsWaitingForBeforeUnloadACK(FrameTreeNode* frame_tree_node);
+
  protected:
   friend class base::RefCounted<Navigator>;
   virtual ~Navigator() {}