Prepare fullscreen_chromeos.cc to be used for ozone builds.

chrome/browser/fullscreen_chromeos.cc

-// Copyright (c) 2013 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/fullscreen.h"
-
-#include "ash/root_window_controller.h"
-#include "chrome/browser/ui/ash/ash_util.h"
-
-bool IsFullScreenMode() {
-  if (chrome::IsRunningInMash()) {
-    // TODO: http://crbug.com/640390.
-    NOTIMPLEMENTED();
-    return false;
-  }
-  // TODO(oshima): Fullscreen is per display state. Investigate
-  // and fix if necessary.
-  ash::RootWindowController* controller =
-      ash::RootWindowController::ForTargetRootWindow();
-  return controller && controller->GetWindowForFullscreenMode();
-}