Enable runtime switching between ChromeVox and ChromeVox next via command line.

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 1483 matching lines @@
     'ozone_platform_egltest%': 0,
     'ozone_platform_gbm%': 0,
     'ozone_platform_ozonex%': 0,
     'ozone_platform_test%': 0,
 
     # Chrome OS: whether to build ChromeVox from sources in the Chromium
     # repository rather than using precompiled JavaScript in
     # chrome/third_party/chromevox.  This is still experimental.
     'use_migrated_chromevox%': 1,
 
-    # Chrome OS: whether to also build the upcoming version of
-    # ChromeVox, which can then be enabled via a command-line switch.
-    'use_chromevox_next%': 0,
-
     'conditions': [
       # Enable the Syzygy optimization step for the official builds.
       ['OS=="win" and buildtype=="Official" and syzyasan!=1', {
         'syzygy_optimize%': 1,
       }, {
         'syzygy_optimize%': 0,
       }],
       # Get binutils version so we can enable debug fission if we can.
       ['os_posix==1 and OS!="mac" and OS!="ios"', {
         'conditions': [
@@ skipping 4265 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',
   },
 }