Reenable linux_aura on the main builders. (Again).

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 66 matching lines @@
             ['chromeos==1 or OS=="win"', {
               'use_ash%': 1,
               'use_aura%': 1,
             }],
 
             # Ozone uses Aura.
             ['use_ozone==1', {
               'use_aura%': 1,
             }],
 
+            # ToT Linux should be aura.
+            #
+            # TODO(erg): Merge this into the previous block once compiling with
+            # aura safely implies including ash capabilities.
+            ['OS=="linux"', {
+              'use_aura%': 1,
+            }],
+
             # Whether we're a traditional desktop unix.
             ['(OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="solaris") and chromeos==0', {
               'desktop_linux%': 1,
             }, {
               'desktop_linux%': 0,
             }],
 
             # Compute the architecture that we're building on.
             ['OS=="win" or OS=="mac" or OS=="ios"', {
               'host_arch%': 'ia32',
@@ skipping 4737 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',
   },
 }