Fix mangling of local variables when their name conflict with Dart2JS's temporaries.

tests/language/src/TempManglingTest.dart

Index: tests/language/src/TempManglingTest.dart
===================================================================
--- tests/language/src/TempManglingTest.dart	(revision 0)
+++ tests/language/src/TempManglingTest.dart	(revision 0)
@@ -0,0 +1,31 @@
+// 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.
+
+main() {
+  testOne();
+  testTwo();
+}
+
+testOne() {
+  // Dart2JS uses t[0-9]* to declare temporaries, so a local variable
+  // with that pattern can conflict with them.
+  var t0 = new List();
+  // By using 'is' check, we make sure 't0.length' does not become
+  // generate at use site.
+  Expect.isTrue(t0.length is int);
+  Expect.isTrue(t0 is List);
+}
+
+testTwo() {
+  var x = new List();
+  var x_0 = new List();
+  {
+    // This used to introduce x_0.
+    var x = new Set();
+    Expect.equals(0, x.length);
+    Expect.isTrue(x.isEmpty());
+  }
+  Expect.isTrue(x is List);
+  Expect.isTrue(x_0 is List);
+}