Support using a Mojo message pipe in a ChannelHandle.

ipc/ipc_mojo_param_traits.cc

Index: ipc/ipc_mojo_param_traits.cc
diff --git a/ipc/ipc_mojo_param_traits.cc b/ipc/ipc_mojo_param_traits.cc
index af79f3b9ae6515ee5a7012be2ff3fb746d00b0fa..a529c97e361c9d9b9c967bb6113563140f0ec495 100644
--- a/ipc/ipc_mojo_param_traits.cc
+++ b/ipc/ipc_mojo_param_traits.cc
@@ -9,6 +9,13 @@
 
 namespace IPC {
 
+void ParamTraits<mojo::MessagePipeHandle>::GetSize(base::PickleSizer* sizer,
+                                                   const param_type& p) {
+  sizer->AddBool();

[dcheng, 2016/06/24 07:50:48]

Nit: GetParamSize(sizer, p.is_valid())

[Anand Mistry (off Chromium), 2016/06/27 00:46:24]

Done.

+  if (p.is_valid())
+    sizer->AddAttachment();
+}
+
 void ParamTraits<mojo::MessagePipeHandle>::Write(Message* m,
                                                  const param_type& p) {
   WriteParam(m, p.is_valid());