Implement accessing lazily initialized static fields.

dart/sdk/lib/_internal/compiler/implementation/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;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked;
 
   JavaScriptItemCompilationContext()
@@ skipping 1411 matching lines @@
   /// Called when [:new Symbol(...):] is seen.
   void registerNewSymbol(TreeElements elements) {
   }
 
   bool retainGetter(Element element) => isTreeShakingDisabled;
 
   bool retainSetter(Element element) => isTreeShakingDisabled;
 
   bool retainName(SourceString name) => mustPreserveNames;
 
+  bool get rememberLazies => isTreeShakingDisabled;
+
   bool retainMetadataOf(Element element) {
     if (mustRetainMetadata) {
       // TODO(ahe): This is a little hacky, but I'll have to rewrite this when
       // implementing @MirrorsUsed anyways.
       compiler.constantHandler.compiledConstants.addAll(
           compiler.metadataHandler.compiledConstants);
       compiler.metadataHandler.compiledConstants.clear();
     }
     if (mustRetainMetadata) hasRetainedMetadata = true;
     return mustRetainMetadata;
@@ skipping 36 matching lines @@
   }
 }
 
 /// Records that [type] is used by [user.element].
 class Dependency {
   final DartType type;
   final TreeElements user;
 
   const Dependency(this.type, this.user);
 }