Revert 187427 "PPAPI: Remove threading options; it's always on"

ppapi/ppapi_proxy.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.
 
 {
   'target_defaults': {
     'variables': {
       'ppapi_proxy_target': 0,
     },
     'target_conditions': [
@@ skipping 51 matching lines @@
           'proxy/host_dispatcher.cc',
           'proxy/host_dispatcher.h',
           'proxy/host_resolver_private_resource.cc',
           'proxy/host_resolver_private_resource.h',
           'proxy/host_var_serialization_rules.cc',
           'proxy/host_var_serialization_rules.h',
           'proxy/interface_list.cc',
           'proxy/interface_list.h',
           'proxy/interface_proxy.cc',
           'proxy/interface_proxy.h',
-          'proxy/locking_resource_releaser.h',
           'proxy/plugin_array_buffer_var.cc',
           'proxy/plugin_array_buffer_var.h',
           'proxy/plugin_dispatcher.cc',
           'proxy/plugin_dispatcher.h',
           'proxy/plugin_globals.cc',
           'proxy/plugin_globals.h',
           'proxy/plugin_main_nacl.cc',
           'proxy/plugin_message_filter.cc',
           'proxy/plugin_message_filter.h',
           'proxy/plugin_resource.cc',
@@ skipping 133 matching lines @@
               'proxy/serialized_flash_menu.cc',
               'proxy/talk_resource.cc',
               'proxy/video_capture_resource.cc',
             ],
           }],
         ],
       }],
     ],
   },
 }