Use Mojo pipes to signal sync IPC events

mojo/public/cpp/bindings/BUILD.gn

 # Copyright 2014 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.
 
 source_set("bindings") {
   sources = [
     "array.h",
     "array_traits.h",
     "array_traits_carray.h",
     "array_traits_standard.h",
@@ skipping 66 matching lines @@
     "lib/scoped_interface_endpoint_handle.cc",
     "lib/serialization.h",
     "lib/serialization_context.cc",
     "lib/serialization_context.h",
     "lib/serialization_forward.h",
     "lib/serialization_util.cc",
     "lib/serialization_util.h",
     "lib/string_serialization.h",
     "lib/string_traits_string16.cc",
     "lib/sync_handle_registry.cc",
-    "lib/sync_handle_registry.h",
     "lib/sync_handle_watcher.cc",
     "lib/sync_handle_watcher.h",
     "lib/union_accessor.h",
     "lib/validate_params.h",
     "lib/validation_errors.cc",
     "lib/validation_errors.h",
     "lib/validation_util.cc",
     "lib/validation_util.h",
     "map.h",
     "map_traits.h",
     "map_traits_standard.h",
     "map_traits_stl.h",
     "message.h",
     "message_filter.h",
     "native_enum.h",
     "native_struct.h",
     "no_interface.h",
     "scoped_interface_endpoint_handle.h",
     "stl_converters.h",
     "string.h",
     "string_traits.h",
     "string_traits_standard.h",
     "string_traits_stl.h",
     "string_traits_string16.h",
     "string_traits_string_piece.h",
     "strong_binding.h",
     "struct_ptr.h",
+    "sync_handle_registry.h",
     "type_converter.h",
   ]
 
   public_deps = [
     ":callback",
     ":struct_traits",
     "//base",
     "//ipc:param_traits",
     "//mojo/public/cpp/system",
   ]
@@ skipping 38 matching lines @@
     ]
 
     public_deps = [
       ":bindings",
       "//third_party/WebKit/Source/wtf",
     ]
 
     public_configs = [ "//third_party/WebKit/Source:config" ]
   }
 }