Support type promotion in dart2js.

tests/language/type_promotion_more_specific_test.dart

Index: tests/language/type_promotion_more_specific_test.dart
diff --git a/tests/language/type_promotion_more_specific_test.dart b/tests/language/type_promotion_more_specific_test.dart
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+// 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 use of more specific in type promotion of interface types.
+
+class A {
+  var a;
+}
+
+class B extends A {
+  var b;
+}
+
+class C {
+  var c;
+}
+
+class D<T> {
+  T d;
+
+  D(this.d);
+}
+
+class E<T> extends D<T> {
+  T e;
+
+  E(e) : this.e = e, super(e);
+}
+
+void main() {
+  testInterface();
+  testGeneric();
+}
+
+void testInterface() {
+  var x;
+  var y;
+
+  A a = new B();
+  if (a is B) { // Promotion B << A.
+    x = a.b; /// 01: ok
+  }
+  if (a is C) { // No promotion C !<< A.
+    x = a.c; /// 02: static type warning
+  }
+  B b = new B();
+  if (b is A) { // No promotion B !<< A.
+    x = b.b; /// 03: ok
+  }
+  if (x is A) { // No promotion A !<< dynamic.
+    y = x.b; /// 04: ok
+  }
+}
+
+testGeneric() {
+  var x;
+  var y;
+
+  D d1 = new E<B>(null);
+  if (d1 is E) { // Promotion: E << D.
+    x = d1.e; /// 05: ok
+  }
+  if (d1 is E<A>) { // No promotion E<A> << D.
+    int a = d1.d; /// 06: ok
+    String b = d1.d; /// 07: ok
+    x = d1.e; /// 08: static type warning
+  }
+
+  D<A> d2 = new E<B>(null);
+  if (d2 is E) { // Promotion: E << D<A>
+    x = d2.e; /// 09: ok
+    int a = d2.e; /// 10: ok
+    String b = d2.e; /// 11: ok
+  }
+
+  D<A> d3 = new E<B>(new B());
+  if (d3 is E<B>) { // Promotion: E<B> << D<A>
+    x = d3.d.b; /// 12: ok
+    x = d3.e.b; /// 13: ok
+  }
+}