Use instrumented libc++ by default in TSan builds.

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 1891 matching lines @@
       ['asan==1 and OS=="mac"', {
         # TODO(glider): we do not strip ASan binaries until the dynamic ASan
         # runtime is fully adopted. See http://crbug.com/242503.
         'mac_strip_release': 0,
       }],
       ['lsan==1', {
         'clang%': 1,
       }],
       ['tsan==1', {
         'clang%': 1,
+        'use_custom_libcxx%': 1,
       }],
       ['msan==1', {
         'clang%': 1,
       }],
 
       ['OS=="linux" and clang_type_profiler==1', {
         'clang%': 1,
         'clang_use_chrome_plugins%': 0,
         'conditions': [
           ['host_arch=="x64"', {
@@ skipping 3287 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',
   },
 }