Support non-const instance field initializers.

lib/compiler/implementation/resolver.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.
 
 interface TreeElements {
   Element operator[](Node node);
   Selector getSelector(Send send);
   Type getType(TypeAnnotation annotation);
 }
 
@@ skipping 912 matching lines @@
   bool inInstanceContext;
   Scope scope;
   ClassElement currentClass;
   bool typeRequired = false;
   StatementScope statementScope;
   int allowedCategory = ElementCategory.VARIABLE | ElementCategory.FUNCTION;
 
   ResolverVisitor(Compiler compiler, Element element)
     : this.mapping  = new TreeElementMapping(),
       this.enclosingElement = element,
-      inInstanceContext = element.isInstanceMember()
+      // When the element is a field, we are actually resolving its
+      // initial value, which should not have access to instance
+      // fields.
+      inInstanceContext = (element.isInstanceMember() && !element.isField())
           || element.isGenerativeConstructor(),
       this.currentClass = element.isMember() ?
                               element.getEnclosingClass() :
                               null,
       this.statementScope = new StatementScope(),
       typeResolver = new TypeResolver(compiler),
       scope = element.buildEnclosingScope(),
       super(compiler) {
   }
 
@@ skipping 1635 matching lines @@
   TopScope(LibraryElement library) : super(null, library);
   Element lookup(SourceString name) {
     return library.find(name);
   }
 
   Element add(Element newElement) {
     throw "Cannot add an element in the top scope";
   }
   String toString() => '$element';
 }