Preserve type variables in closure conversion.

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 723 matching lines @@
 type VectorCopy extends Expression {
   Byte tag = 105;
   Expression vectorExpression;
 }
 
 type ClosureCreation extends Expression {
   Byte tag = 106;
   MemberReference topLevelFunctionReference;
   Expression contextVector;
   FunctionType functionType;
+  List<DartType> typeArguments;
 }
 
 abstract type Statement extends Node {}
 
 type InvalidStatement extends Statement {
   Byte tag = 60;
 }
 
 type ExpressionStatement extends Statement {
   Byte tag = 61;
@@ skipping 260 matching lines @@
   Option<DartType> bound;
 }
 
 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.
 }
 
 ```