Add primitive to create closures and use it for 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 663 matching lines @@
   Expression vectorExpression;
   UInt index;
   Expression value;
 }
 
 type VectorCopy extends Expression {
   Byte tag = 105;
   Expression vectorExpression;
 }
 
+type ClosureCreation extends Expression {
+  Byte tag = 106;
+  String topLevelFunctionName;

[asgerf, 2017/03/31 11:03:41]

This should be a MemberReference

[Dmitry Stefantsov, 2017/03/31 11:54:13]

Thanks! Done.

+  Expression contextVector;
+  FunctionType functionType;
+}
+
 abstract type Statement extends Node {}
 
 type InvalidStatement extends Statement {
   Byte tag = 60;
 }
 
 type ExpressionStatement extends Statement {
   Byte tag = 61;
   Expression expression;
 }
@@ skipping 246 matching lines @@
   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.
 }
 
 ```