Add command line switch for enabling threaded compositing

build/common.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.
 
 # 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 935 matching lines @@
         'defines': ['ENABLE_PROFILING=1'],
       }],
       ['OS=="linux" and glibcxx_debug==1', {
         'defines': ['_GLIBCXX_DEBUG=1',],
         'cflags_cc!': ['-fno-rtti'],
         'cflags_cc+': ['-frtti', '-g'],
       }],
       ['remoting==1', {
         'defines': ['ENABLE_REMOTING=1'],
       }],
-      ['use_threaded_compositing==1', {
-        'defines': ['WTF_USE_THREADED_COMPOSITING'],
-      }],
       ['p2p_apis==1', {
         'defines': ['ENABLE_P2P_APIS=1'],
       }],
       ['proprietary_codecs==1', {
         'defines': ['USE_PROPRIETARY_CODECS'],
       }],
       ['enable_flapper_hacks==1', {
         'defines': ['ENABLE_FLAPPER_HACKS=1'],
       }],
       ['configuration_policy==1', {
@@ skipping 1523 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',
   },
 }