Add message sizing to basic IPC traits and struct macros.

mojo/public/cpp/bindings/tests/pickled_struct_chromium.cc

Index: mojo/public/cpp/bindings/tests/pickled_struct_chromium.cc
diff --git a/mojo/public/cpp/bindings/tests/pickled_struct_chromium.cc b/mojo/public/cpp/bindings/tests/pickled_struct_chromium.cc
index d45a44a51f837945155555688c60d1929983a884..0dee03f753c47175312a1ecbca223ee17b0e003d 100644
--- a/mojo/public/cpp/bindings/tests/pickled_struct_chromium.cc
+++ b/mojo/public/cpp/bindings/tests/pickled_struct_chromium.cc
@@ -22,6 +22,13 @@ PickledStructChromium::~PickledStructChromium() {}
 
 namespace IPC {
 
+void ParamTraits<mojo::test::PickledStructChromium>::GetSize(
+    base::PickleSizer* sizer,
+    const param_type& p) {
+  sizer->AddInt();
+  sizer->AddInt();
+}
+
 void ParamTraits<mojo::test::PickledStructChromium>::Write(
     base::Pickle* m,
     const param_type& p) {