Add an optional bound to type parameter references

pkg/kernel/binary.md

 This file describes the binary format of Dart Kernel.
 
 Notation
 --------
 Bitmasks are described with the syntax:
 ```scala
     Byte flags (flag1, flag2, ..., flagN)
 ```
 where 'flag<N>' is the N-th least significant bit,
 (so flag1 is the least significant bit).
@@ skipping 931 matching lines @@
   // from the definition of scoping, since type parameter N+1 is not "in scope"
   // in the bound of type parameter N, but it takes up an index as if it was in
   // scope there.
   //
   // The type parameter can be bound by a Class, FunctionNode, or FunctionType.
   //
   // Note that constructors currently do not declare type parameters.  Uses of
   // the class type parameters in a constructor refer to those declared on the
   // class.
   UInt index;
+  
+  Option<DartType> bound;
 }
 
 type VectorType extends DartType {
   Byte tag = 88;
 }
 
 type TypeParameter {
   // Note: there is no tag on TypeParameter
   StringReference name; // Cosmetic, may be empty, not unique.
   DartType bound; // 'dynamic' if no explicit bound was given.
 }
 
 ```