third_party: Add the libsync library from Android

third_party/libsync/libsync.gyp

+# Copyright 2016 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.
+
+{
+  'targets': [
+    {
+      'target_name': 'libsync',
+      'type': 'static_library',
+      'sources': [
+        'include/linux/sw_sync.h',
+        'include/linux/sync.h',
+        'include/sw_sync.h',
+        'include/sync/sync.h',
+        'sync.c',
+      ],
+      'include_dirs': [
+        'include',
+      ],
+      # TODO(reveman): Remove this when crbug.com/591791 has been fixed.
+      'defines': ['strlcpy=strncpy'],
+      'direct_dependent_settings': {
+        'include_dirs': [
+          'include',
+        ],
+      },
+    },
+  ],
+}