Don't allow statement-nodes in expression contexts.

tests/language/side_effect_throw_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.
+
+class B {
+  static var x;
+  operator <<(other) {
+    x = other;
+    return 33;
+  }
+}
+
+class A {
+  get _m() => new B();
+  opshl(n) {
+    // 'n' must be a number, but we are not allowed throw throw before we have

[ngeoffray, 2012/08/17 13:08:58]

throw throw -> to throw

[floitsch, 2012/08/29 11:03:12]

Done.

+    // evaluated _m << 499.
+    return (_m << 499) | (2 - n);
+  }
+}
+
+main() {
+  var a = new A();
+  Expect.throws(() => a.opshl("string"));
+  Expect.equals(499, B.x);
+}