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': [
     {
-      # GN version: //ios/third_party/fishhook
-      'target_name': 'fishhook',
+      'target_name': 'libsync',
       'type': 'static_library',
       'sources': [
-        'src/fishhook.c',
-        'src/fishhook.h',
+        'include/linux/sw_sync.h',
+        'include/linux/sync.h',
+        'include/sw_sync.h',
+        'include/sync/sync.h',
+        'strlcpy.c',
+        'sync.c',
+      ],
+      'include_dirs': [
+        'include',
       ],
       'direct_dependent_settings': {
         'include_dirs': [
-          'src'
+          'include',
         ],
       },
     },
   ],
 }