Disallow `null` in spanFromSpannable.

pkg/compiler/lib/src/resolution/class_hierarchy.dart

 // Copyright (c) 2015, 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.class_hierarchy;
 
 import '../common.dart';
 import '../common/resolution.dart' show Resolution;
 import '../core_types.dart' show CoreClasses, CoreTypes;
 import '../dart_types.dart';
@@ skipping 464 matching lines @@
   }
 
   Link<DartType> resolveInterfaces(NodeList interfaces, Node superclass) {
     Link<DartType> result = const Link<DartType>();
     if (interfaces == null) return result;
     for (Link<Node> link = interfaces.nodes; !link.isEmpty; link = link.tail) {
       DartType interfaceType = resolveType(link.head);
       if (interfaceType != null) {
         if (interfaceType.isMalformed) {
           reporter.reportErrorMessage(
-              superclass,
+              link.head,
               MessageKind.CANNOT_IMPLEMENT_MALFORMED,
               {'className': element.name, 'malformedType': interfaceType});
         } else if (interfaceType.isEnumType) {
           reporter.reportErrorMessage(
-              superclass,
+              link.head,
               MessageKind.CANNOT_IMPLEMENT_ENUM,
               {'className': element.name, 'enumType': interfaceType});
         } else if (!interfaceType.isInterfaceType) {
           // TODO(johnniwinther): Handle dynamic.
           TypeAnnotation typeAnnotation = link.head;
           reporter.reportErrorMessage(
               typeAnnotation.typeName, MessageKind.CLASS_NAME_EXPECTED);
         } else {
           if (interfaceType == element.supertype) {
             reporter.reportErrorMessage(
@@ skipping 144 matching lines @@
     Identifier selector = node.selector.asIdentifier();
     var e = prefixElement.lookupLocalMember(selector.source);
     if (e == null || !e.impliesType) {
       reporter.reportErrorMessage(node.selector,
           MessageKind.CANNOT_RESOLVE_TYPE, {'typeName': node.selector});
       return;
     }
     loadSupertype(e, node);
   }
 }