Add Vector type to Kernel

pkg/kernel/testcases/closures/named_closure.dart.expect

 library;
 import self as self;
 import "dart:core" as core;
-import "dart:mock" as mock;
 
 class Closure#main#g extends core::Object implements core::Function {
   field core::String note = "This is temporary. The VM doesn't need closure classes.";
-  field mock::Context context;
-  constructor •(final mock::Context context) → dynamic
+  field Vector context;
+  constructor •(final Vector context) → dynamic
     : self::Closure#main#g::context = context
     ;
   method call(dynamic x) → dynamic {
     "This is a temporary solution. In the VM, this will become an additional parameter.";
-    final mock::Context #contextParameter = this.{self::Closure#main#g::context};
-    return #contextParameter.[](0).[](x);
+    final Vector #contextParameter = this.{self::Closure#main#g::context};
+    return (#contextParameter[1]).[](x);
   }
 }
 static field dynamic f = null;
 static method foo() → dynamic {
   core::print(self::f.call(0));
 }
 static method main(dynamic arguments) → dynamic {
-  final mock::Context #context = new mock::Context::•(1);
-  #context.[]=(0, arguments);
+  final Vector #context = MakeVector(2);
+  #context[1] = arguments;
   final (dynamic) → dynamic g = new self::Closure#main#g::•(#context);
   self::f = g;
   self::foo();
 }