vdl: Add TODOs to handle embedded struct fields.

Go 1.6 changed the behavior of unexported embedded struct fields.
I was worried that this might break our existing code, but as it
turns out, we never really handled unexported embedded struct
fields anyways.  Note that the unexported embedded struct field
may itself have exported fields, which would take extra logic to
handle correctly.

It seems fine to ignore these for now.  VDL will never generate
structs with (unexported or exported) embedded struct fields.
Technically the user could provide us a non-vdl generated Go
struct with embedded struct fields that have exported fields, but
that seems rare enough to ignore for now.

Issue v.io/i/1218

Change-Id: Ia4b65239308e4559c9cff06c17bf9db4300b21fa
diff --git a/vdl/convert.go b/vdl/convert.go
index 57b53c4..3716118 100644
--- a/vdl/convert.go
+++ b/vdl/convert.go
@@ -1343,6 +1343,9 @@
 				ttField, _ := tt.FieldByName(name)
 				return reflectConv(c.rv.FieldByName("Value"), ttField.Type)
 			}
+			// TODO(toddw): How should we handle anonymous (aka embedded) fields?
+			// Note that unexported embedded fields may themselves have exported
+			// fields.  See https://github.com/golang/go/issues/12367
 			rvField := c.rv.FieldByName(key.rv.String())
 			ttField, index := tt.FieldByName(key.rv.String())
 			if !rvField.IsValid() || index < 0 {
diff --git a/vdl/reflect_type.go b/vdl/reflect_type.go
index 2c05a54..9d8b736 100644
--- a/vdl/reflect_type.go
+++ b/vdl/reflect_type.go
@@ -380,6 +380,9 @@
 	case reflect.Struct:
 		st := builder.Struct()
 		for fx := 0; fx < rt.NumField(); fx++ {
+			// TODO(toddw): How should we handle anonymous (aka embedded) fields?
+			// Note that unexported embedded fields may themselves have exported
+			// fields.  See https://github.com/golang/go/issues/12367
 			rtField := rt.Field(fx)
 			if rtField.PkgPath != "" {
 				continue // field isn't exported