Allow function literals in string interpolation

tests/language/function_literals2_test.dart

 // Copyright (c) 2011, 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 for new function type alias.
 
 import "package:expect/expect.dart";
 
 class FunctionLiteralsTest {
 
@@ skipping 28 matching lines @@
     Expect.equals(false, isOdd(8));
 
     var b = new B(10);
     Expect.equals(10, b.n);
     Expect.equals(100, (b.f)(10));
 
     b = new B.withZ(10);
     Expect.equals(10, b.n);
     Expect.equals(101, (b.f)(10));
 
+    var c = new C(5);
+    Expect.equals("2*x is 10", c.s);
+
     int x = 0;
     int y = 1;
     // make sure this isn't parsed as a generic type
     Expect.isTrue(x<y, "foo");
   }
 }
 
 apply(f, n) {
   return f(n);
 }
 
 bool isOdd(b) => b % 2 == 1;
 
 class A {
   int f;
   int f2;
   A(p) : f = apply((j) => 2 - j, p) { /* constr. body */ f2 = -p; }
   A.n(p) : f = 1 + apply((j) => 2 - j, p) { /* constr. body */ f2 = -f; }
 }
 
 class B {
   var f;
   int n;
   B(z) : f = ((x) => x * x) { n = z; }
   B.withZ(z) : f = ((x) { return x * x + 1; }) { n = z; }
 }
 
+class C {
+  String s;
+  C(x) : s = "2*x is ${() { return 2*x; }()}";
+}
 main() {
   FunctionLiteralsTest.testMain();
 }