Introduce initial plumbing for type promotion in fasta.

pkg/front_end/testcases/implicit_scope_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.
+// Test that if, while etc create an implicit scope if the body
+// is not a compound statement.
+
+import "package:expect/expect.dart";
+
+class ImplicitScopeTest {
+  static bool alwaysTrue() {
+    return 1 + 1 == 2;
+  }
+
+  static testMain() {
+    var a = "foo";
+    var b;
+    if (alwaysTrue())
+      var a = "bar";
+    else
+      var b = a;
+    Expect.equals("foo", a);
+    Expect.equals(null, b);
+
+    while (!alwaysTrue()) var a = "bar", b = "baz";
+    Expect.equals("foo", a);
+    Expect.equals(null, b);
+
+    for (int i = 0; i < 10; i++) var a = "bar", b = "baz";
+    Expect.equals("foo", a);
+    Expect.equals(null, b);
+
+    do var a = "bar", b = "baz"; while ("black" == "white");
+    Expect.equals("foo", a);
+    Expect.equals(null, b);
+  }
+}
+
+main() {
+  ImplicitScopeTest.testMain();
+}