Detect dead code, and handle breaks and continues in inferrer.

tests/language/inferrer_constructor_test.dart

+// Copyright (c) 2013, 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.
+
+// Test that dart2js type inferrer detects dead code.
+
+import "package:expect/expect.dart";
+
+class A {
+  var field;
+  A(test) {
+    if (test) {
+      return;
+      field = 42;
+    } else {
+      field = 54;
+    }
+  }
+}
+
+main() {
+  var a = new A(true);
+  Expect.throws(() => a.field + 42, (e) => e is NoSuchMethodError);
+}