Handle fields with initializers in kernel_impact

pkg/compiler/lib/src/resolution/resolution.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.
 
 library dart2js.resolution;
 
 import 'dart:collection' show Queue;
 
 import '../common.dart';
 import '../common/names.dart' show Identifiers;
@@ skipping 412 matching lines @@
       // Perform various checks as side effect of "computing" the type.
       element.computeType(resolution);
 
       resolution.target.resolveNativeElement(element, registry.impactBuilder);
 
       return registry.impactBuilder;
     });
   }
 
   DartType resolveTypeAnnotation(Element element, TypeAnnotation annotation) {
-    DartType type = resolveReturnType(element, annotation);
+    DartType type = _resolveReturnType(element, annotation);
     if (type.isVoid) {
       reporter.reportErrorMessage(annotation, MessageKind.VOID_NOT_ALLOWED);
     }
     return type;
   }
 
-  DartType resolveReturnType(Element element, TypeAnnotation annotation) {
+  DartType _resolveReturnType(Element element, TypeAnnotation annotation) {
     if (annotation == null) return const DynamicType();
     DartType result = visitorFor(element).resolveTypeAnnotation(annotation);
+    assert(invariant(annotation, result != null,
+        message: "No type computed for $annotation."));
     if (result == null) {
       // TODO(karklose): warning.
       return const DynamicType();
     }
     return result;
   }
 
   void resolveRedirectionChain(ConstructorElement constructor, Spannable node) {
     ConstructorElement target = constructor;
     DartType targetType;
@@ skipping 669 matching lines @@
   TreeElements get treeElements {
     assert(invariant(this, _treeElements != null,
         message: "TreeElements have not been computed for $this."));
     return _treeElements;
   }
 
   void reuseElement() {
     _treeElements = null;
   }
 }