Prepare fullscreen_chromeos.cc to be used for ozone builds.

chrome/browser/fullscreen_chromeos_or_ozone.cc

-// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Copyright (c) 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/fullscreen.h"
 
 #include "ash/root_window_controller.h"
 #include "chrome/browser/ui/ash/ash_util.h"
 
 bool IsFullScreenMode() {
-  if (chrome::IsRunningInMash()) {
+#if defined(USE_ASH)

[sky, 2016/10/26 17:37:15]

I'm confused by what conditions this code would be used in. You have a USE_ASH
check here, but then line 22 is using ash too. So, I'm confused.

[fwang, 2016/10/31 11:38:49]

Yes, USE_ASH is very confusing as ash can be built without this flag enabled and
CHROMEOS is often used as an equivalent of it (see for example
https://codereview.chromium.org/2408803002/#msg25)

Additionally, when USE_ASH is false, the mentioned code will never be executed
(and maybe some compilers will complain about dead code).

I wonder whether Robert's suggestion on
https://codereview.chromium.org/2408803002/#msg49 is really the right thing to
do and whether we should just have a separate fullscreen_ozone file for ozone
instead?

+  if (chrome::IsRunningInMash())
+#endif
+  {
     // 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();
 }