Fix duplicate context creation when closures appear in initializers.

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

Index: pkg/kernel/testcases/closures/closure_in_constructor.dart.expect
diff --git a/pkg/kernel/testcases/closures/closure_in_constructor.dart.expect b/pkg/kernel/testcases/closures/closure_in_constructor.dart.expect
index 2e3a64712f01c3a6e34ecff2aec190e4a101a4b2..d83238b4c63708cef3857106d56f50738f7eefec 100644
--- a/pkg/kernel/testcases/closures/closure_in_constructor.dart.expect
+++ b/pkg/kernel/testcases/closures/closure_in_constructor.dart.expect
@@ -11,9 +11,10 @@ class C1 extends core::Object {
 class C2 extends core::Object {

[Dmitry Stefantsov, 2017/07/28 12:36:16]

If I'm getting this right, here is the Dart code for this class:

```
class C2 {
  var x;
  C2(y) {
    x = () => print('Hello $y');
  }
}
```

My understanding is that we shouldn't apply this technique with redirecting
constructors here, because there are no initializers.

[sjindel, 2017/07/31 12:06:21]

Done.

   field dynamic x = null;
   constructor •(dynamic y) → void
-    : final Vector #context = MakeVector(2), dynamic #t2 = #context[1] = y, super core::Object::•() {
-    final Vector #context = MakeVector(2);
-    #context[1] = y;
+    : final Vector #context = MakeVector(2), this self::C2::#redir(y, #context)
+    ;
+  constructor #redir(dynamic y, final Vector #context) → void
+    : dynamic #t2 = #context[1] = y, super core::Object::•() {
     this.x = MakeClosure<() → dynamic>(self::closure#C2#function#function, #context);
   }
 }