Refactor WindowFinder definition

chrome/browser/ui/views/tabs/window_finder.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/views/tabs/window_finder.h"
 
-WindowFinder::WindowFinder() {}
-WindowFinder::~WindowFinder() {}
+#include "chrome/browser/ui/views/tabs/window_finder_mus.h"
+
+gfx::NativeWindow GetLocalProcessWindowAtPointImpl(
+    const gfx::Point& screen_point,
+    const std::set<gfx::NativeWindow>& ignore);
+
+gfx::NativeWindow WindowFinder::GetLocalProcessWindowAtPoint(
+    const gfx::Point& screen_point,
+    const std::set<gfx::NativeWindow>& ignore) {
+
+  gfx::NativeWindow out;
+  if (GetLocalProcessWindowAtPointMus(screen_point, ignore, &out))
+    return out;
+
+  return GetLocalProcessWindowAtPointImpl(screen_point, ignore);
+}