Remove unused method declaration - IsLikelyAutoNavigation.

Just dead code cleanup.

BUG=
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2176203004
Cr-Commit-Position: refs/heads/master@{#407643}

content/browser/frame_host/navigation_controller_impl.h

@@ -345,10 +345,6 @@ class CONTENT_EXPORT NavigationControllerImpl
   // true before calling this.
   void PruneAllButLastCommittedInternal();
 
-  // Returns true if the navigation is likley to be automatic rather than
-  // user-initiated.
-  bool IsLikelyAutoNavigation(base::TimeTicks now);
-
   // Inserts up to |max_index| entries from |source| into this. This does NOT
   // adjust any of the members that reference entries_
   // (last_committed_entry_index_, pending_entry_index_ or