Implement NativeAppWindowGtk::IsFullscreen.

chrome/browser/ui/gtk/extensions/native_app_window_gtk.cc

 // Copyright (c) 2012 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/gtk/extensions/native_app_window_gtk.h"
 
 #include "base/utf_string_conversions.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/gtk/extensions/extension_keybinding_registry_gtk.h"
 #include "chrome/browser/ui/gtk/gtk_util.h"
@@ skipping 139 matching lines @@
 
 bool NativeAppWindowGtk::IsMaximized() const {
   return (state_ & GDK_WINDOW_STATE_MAXIMIZED);
 }
 
 bool NativeAppWindowGtk::IsMinimized() const {
   return (state_ & GDK_WINDOW_STATE_ICONIFIED);
 }
 
 bool NativeAppWindowGtk::IsFullscreen() const {
-  return false;
+  return (state_ & GDK_WINDOW_STATE_FULLSCREEN);
 }
 
 gfx::NativeWindow NativeAppWindowGtk::GetNativeWindow() {
   return window_;
 }
 
 gfx::Rect NativeAppWindowGtk::GetRestoredBounds() const {
   gfx::Rect window_bounds = restored_bounds_;
   window_bounds.Inset(-GetFrameInsets());
   return window_bounds;
@@ skipping 341 matching lines @@
 
   draggable_region_.reset(ShellWindow::RawDraggableRegionsToSkRegion(regions));
 }
 
 // static
 NativeAppWindow* NativeAppWindow::Create(
     ShellWindow* shell_window,
     const ShellWindow::CreateParams& params) {
   return new NativeAppWindowGtk(shell_window, params);
 }