fix cascade on ThisExpression

test/codegen/language/cascade_in_expression_function_test.dart

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+// Dart test program for testing throw statement
+
+import "package:expect/expect.dart";
+
+makeMap() => new Map()..[3] = 4 ..[0] = 11;
+
+class MyClass {
+  foo() => this..bar(3)..baz(4);
+  bar(x) => x;
+  baz(y) => y*2;
+}
+
+main() {
+  var o = new MyClass();
+  Expect.equals(o.foo(), o);
+  var g = makeMap();
+  Expect.equals(g[3], 4);
+  Expect.equals(g[0], 11);
+}