Use Mojo pipes to signal sync IPC events

ppapi/proxy/BUILD.gn

 # Copyright 2015 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.
 
 import("//build/config/nacl/config.gni")
 
 config("proxy_implementation") {
   defines = [ "PPAPI_PROXY_IMPLEMENTATION" ]
 }
 
@@ skipping 265 matching lines @@
 
   public_deps = [
     "//ppapi/proxy:ipc_sources",
   ]
 
   deps = [
     "//base",
     "//gpu/command_buffer/client:client_sources_for_ppapi",
     "//ipc",
     "//media:shared_memory_support",
+    "//mojo/edk/system",
     "//ppapi/c",
     "//ppapi/shared_impl",
   ]
 
   if (!is_nacl) {
     deps += [
       "//base/third_party/dynamic_annotations",
       "//gin",
       "//skia",
       "//ui/events:events_base",
@@ skipping 74 matching lines @@
   deps = [
     "//base/test:test_support",
     "//ipc",
     "//ipc:test_support",
     "//ppapi/proxy",
     "//ppapi/shared_impl",
     "//testing/gmock",
     "//testing/gtest",
   ]
 }