Adds more DBC assembler tests

runtime/vm/constants_dbc.h

Index: runtime/vm/constants_dbc.h
diff --git a/runtime/vm/constants_dbc.h b/runtime/vm/constants_dbc.h
index f4144d69b54e61fb3c0e3cd7783c8fb8bdbb69dc..7234022cc3de717e665afdbcf8eeb0ffa87061e8 100644
--- a/runtime/vm/constants_dbc.h
+++ b/runtime/vm/constants_dbc.h
@@ -302,6 +302,12 @@ namespace dart {
 //    match patched call's argument count so that Return instructions continue
 //    to work.
 //
+//  - LoadClassIdTOS, LoadClassId rA, D
+//
+//    LoadClassIdTOS loads the class id from the object at SP[0] and stores it
+//    to SP[0]. LoadClassId loads the class id from FP[rA] and stores it to
+//    FP[D].
+//
 // TODO(vegorov) the way we replace calls with DebugBreak does not work
 //               with our smi fast paths because DebugBreak is simply skipped.
 //