Define os_posix in gyp files to get new Unix platforms added quickly

build/features_override.gypi

 # 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.
 
 # This file is only included in full-chromium builds, and overrides the
 # feature_defines variable in
 # third_party/WebKit/Source/WebKit/chromium/features.gypi.
 {
   'variables': {
     # WARNING: This list of strings completely replaces the list in
@@ skipping 70 matching lines @@
       'use_threaded_compositing%': 0,
       'enable_svg%': 1,
       'enable_touch_events%': 1,
       'use_skia_gpu%': 0,
     },
     'use_accelerated_compositing%': '<(use_accelerated_compositing)',
     'use_threaded_compositing%': '<(use_threaded_compositing)',
     'enable_svg%': '<(enable_svg)',
     'enable_touch_events%': '<(enable_touch_events)',
     'conditions': [
-      ['(OS=="win" or OS=="linux" or OS=="mac") and use_accelerated_compositing==1', {
+      ['use_accelerated_compositing==1', {
         'feature_defines': [
           'WTF_USE_ACCELERATED_COMPOSITING=1',
           'ENABLE_3D_RENDERING=1',
           'ENABLE_ACCELERATED_2D_CANVAS=1',
         ],
         'use_accelerated_compositing': 1,
       }],
       ['use_accelerated_compositing==1 and use_threaded_compositing==1', {
         'feature_defines': [
           'WTF_USE_THREADED_COMPOSITING=1',
@@ skipping 20 matching lines @@
     # require changes in gyp.
   },
 
 }
 
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 # tab-width:2
 # indent-tabs-mode:nil
 # End:
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