Aura: Desktop aura is now default on non-chromeos linux builds.

build/common.gypi

 # 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 80 matching lines @@
           # Chromeos implies ash.
           ['chromeos==1', {
             'use_ash%': 1,
             'use_aura%': 1,
           }],
 
           # For now, Windows *AND* Linux builds that |use_aura| should also
           # imply using ash. This rule should be removed for the future when
           # both Linux and Windows are using the aura windows without the ash
           # interface.
-          ['use_aura==1 and ((OS=="linux" and chromeos==0) or OS=="win")', {
+          ['use_aura==1 and OS=="win"', {
             'use_ash%': 1,
           }],
           ['use_ash==1', {
             'use_aura%': 1,
           }],
 
           # Set default value of toolkit_views based on OS.
           ['OS=="win" or chromeos==1 or use_aura==1', {
             'toolkit_views%': 1,
           }, {
@@ skipping 2985 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }