Use libc++ by default on iOS

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 786 matching lines @@
           'cld_version%': 1,
           'enable_printing%': 0,
           'enable_session_service%': 0,
           'enable_themes%': 0,
           'enable_webrtc%': 0,
           'notifications%': 0,
           'remoting%': 0,
           'safe_browsing%': 0,
           'enable_managed_users%': 0,
           'enable_task_manager%': 0,
+          'use_system_libcxx%': 1,
         }],
 
         # Use GPU accelerated cross process image transport by default
         # on linux builds with the Aura window manager
         ['use_aura==1 and OS=="linux"', {
           'ui_compositor_image_transport%': 1,
         }, {
           'ui_compositor_image_transport%': 0,
         }],
 
@@ skipping 681 matching lines @@
     # 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': [
-      # The version of clang shipped upstream does not find C++ headers when
-      # using -stdlib=libc++ so we instead need to use the version of clang
-      # coming with Xcode.
-      ['OS=="ios" and use_system_libcxx==1', {
-        'clang_xcode%': 1,
-      }],
       # 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': [
           # compiler_version doesn't work with clang
@@ skipping 4258 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',
   },
 }