Add message sizing to basic IPC traits and struct macros.

mojo/public/cpp/bindings/tests/pickled_struct_blink.h

Index: mojo/public/cpp/bindings/tests/pickled_struct_blink.h
diff --git a/mojo/public/cpp/bindings/tests/pickled_struct_blink.h b/mojo/public/cpp/bindings/tests/pickled_struct_blink.h
index c4406b493d75c1f3ca4c8897c6431f6eb248e61a..ce5b3644d334bef1f0bea017e2a8393ebee91ea0 100644
--- a/mojo/public/cpp/bindings/tests/pickled_struct_blink.h
+++ b/mojo/public/cpp/bindings/tests/pickled_struct_blink.h
@@ -16,6 +16,7 @@
 namespace base {
 class Pickle;
 class PickleIterator;
+class PickleSizer;
 }
 
 namespace mojo {
@@ -61,7 +62,7 @@ template <>
 struct ParamTraits<mojo::test::PickledStructBlink> {
   using param_type = mojo::test::PickledStructBlink;
 
-  static size_t GetSize(const param_type& p) { return 8; }
+  static void GetSize(base::PickleSizer* sizer, const param_type& p);
   static void Write(base::Pickle* m, const param_type& p);
   static bool Read(const base::Pickle* m,
                    base::PickleIterator* iter,