dart2js: fix nondeterministic output of type metadata.

pkg/compiler/lib/src/js_backend/backend.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.
 
 part of js_backend;
 
 const VERBOSE_OPTIMIZER_HINTS = false;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked = new Set<HInstruction>();
@@ skipping 197 matching lines @@
   }
 
   void markAsMustInline(FunctionElement element) {
     _cachedDecisions[element] = _mustInline;
   }
 }
 
 enum SyntheticConstantKind {
   DUMMY_INTERCEPTOR,
   EMPTY_VALUE,
-  TYPEVARIABLE_REFERENCE,
+  TYPEVARIABLE_REFERENCE,  // Reference to a type in reflection data.
   NAME
 }
 
 class JavaScriptBackend extends Backend {
   static final Uri DART_JS_HELPER = new Uri(scheme: 'dart', path: '_js_helper');
   static final Uri DART_INTERCEPTORS =
       new Uri(scheme: 'dart', path: '_interceptors');
   static final Uri DART_FOREIGN_HELPER =
       new Uri(scheme: 'dart', path: '_foreign_helper');
   static final Uri DART_JS_MIRRORS =
@@ skipping 2944 matching lines @@
   }
 }
 
 /// Records that [constant] is used by the element behind [registry].
 class Dependency {
   final ConstantValue constant;
   final Element annotatedElement;
 
   const Dependency(this.constant, this.annotatedElement);
 }