Add libc++ and libc++abi to third-party.

ppapi/ppapi_ipc_untrusted.gyp

 # 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'includes': [
     '../native_client/build/untrusted.gypi',
@@ skipping 18 matching lines @@
             '..',
           ],
           'dependencies': [
             '../native_client/tools.gyp:prep_toolchain',
             '../base/base_untrusted.gyp:base_untrusted',
             '../gpu/gpu_untrusted.gyp:gpu_ipc_untrusted',
             '../ipc/ipc_untrusted.gyp:ipc_untrusted',
             '../ppapi/ppapi_shared_untrusted.gyp:ppapi_shared_untrusted',
             '../components/tracing_untrusted.gyp:tracing_untrusted',
           ],
+          'conditions': [
+            ['use_libcxx==1', {
+              'dependencies!': [
+                '<(DEPTH)/third_party/libc++/libc++.gyp:libc++',
+                '<(DEPTH)/third_party/libc++abi/libc++abi.gyp:libc++abi',
+              ],
+            }],
+          ],
         },
       ],
     }],
   ],
 }