Use Mojo pipes to signal sync IPC events

mojo/mojo_public.gyp

Index: mojo/mojo_public.gyp
diff --git a/mojo/mojo_public.gyp b/mojo/mojo_public.gyp
index 7096de5e890f78561e7431e15d6968ab1d10d683..d9d3ff15b1ff6089db5abd4442b2786c1980755a 100644
--- a/mojo/mojo_public.gyp
+++ b/mojo/mojo_public.gyp
@@ -100,6 +100,8 @@
         'public/cpp/system/buffer.h',
         'public/cpp/system/core.h',
         'public/cpp/system/data_pipe.h',
+        'public/cpp/system/event.cc',
+        'public/cpp/system/event.h',
         'public/cpp/system/functions.h',
         'public/cpp/system/handle.h',
         'public/cpp/system/message.h',
@@ -202,7 +204,6 @@
         'public/cpp/bindings/lib/string_serialization.h',
         'public/cpp/bindings/lib/string_traits_string16.cc',
         'public/cpp/bindings/lib/sync_handle_registry.cc',
-        'public/cpp/bindings/lib/sync_handle_registry.h',
         'public/cpp/bindings/lib/sync_handle_watcher.cc',
         'public/cpp/bindings/lib/sync_handle_watcher.h',
         'public/cpp/bindings/lib/validate_params.h',
@@ -227,6 +228,7 @@
         'public/cpp/bindings/string_traits_string_piece.h',
         'public/cpp/bindings/strong_binding.h',
         'public/cpp/bindings/struct_ptr.h',
+        'public/cpp/bindings/sync_handle_registry.h',
         'public/cpp/bindings/type_converter.h',
         # This comes from the mojo_interface_bindings_cpp_sources dependency.
         '>@(mojom_generated_sources)',