aura: Have aura and aura_demo build and run without gtk on linux.

ui/ui.gyp

 # Copyright (c) 2011 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.
 
 {
   'variables': {
     'chromium_code': 1,
     'toolkit_views2': 0,  # ui/views/ is an experimental framework on Windows.
   },
   'target_defaults': {
@@ skipping 287 matching lines @@
       'conditions': [
         ['use_aura==1', {
           'sources/': [
             ['exclude', 'gfx/gtk_'],
             ['exclude', 'gfx/gtk_util.cc'],
             ['exclude', 'gfx/gtk_util.h'],
             ['exclude', 'gfx/screen_gtk.cc'],
             ['exclude', 'gfx/screen_win.cc'],
             ['exclude', 'base/win/mouse_wheel_util.cc'],
             ['exclude', 'base/win/mouse_wheel_util.h'],
+            ['exclude', 'base/x/active_window_watcher_x.cc'],
+            ['exclude', 'base/x/active_window_watcher_x.h'],
            ],
         }],
         ['use_glib == 1', {
           'dependencies': [
             # font_gtk.cc uses fontconfig.
             '../build/linux/system.gyp:fontconfig',
             '../build/linux/system.gyp:glib',
             '../build/linux/system.gyp:pangocairo',
             '../build/linux/system.gyp:x11',
             '../build/linux/system.gyp:xext',
@@ skipping 34 matching lines @@
             '../build/linux/system.gyp:gtk',
           ],
           'sources': [
             'gfx/gtk_native_view_id_manager.cc',
             'gfx/gtk_native_view_id_manager.h',
             'gfx/gtk_preserve_window.cc',
             'gfx/gtk_preserve_window.h',
             'gfx/gtk_util.cc',
             'gfx/gtk_util.h',
           ],
+          'sources!': [
+            'base/clipboard/clipboard_aura.cc',
+          ],
         }],
         ['use_wayland == 1', {
           'sources/': [
             ['exclude', '_(gtk|x)\\.cc$'],
             ['exclude', '/(gtk|x11)_[^/]*\\.cc$'],
             ['include', 'base/dragdrop/gtk_dnd_util.cc'],
             ['include', 'base/dragdrop/gtk_dnd_util.h'],
             ['include', 'base/dragdrop/os_exchange_data_provider_gtk.cc'],
             ['include', 'base/dragdrop/os_exchange_data_provider_gtk.h'],
             ['include', 'base/keycodes/keyboard_code_conversion_x.cc'],
@@ skipping 169 matching lines @@
                 'shutil.copyfile(\'<(ui_copy_target)\', \'<(ui_copy_dest)\'); ' \
                 'os.chmod(\'<(ui_copy_dest)\', 0700)'
               ]
             }
           ],
         },
       ],
     }],
   ],
 }