Implement line and column numbers.

pkg/front_end/lib/src/fasta/builder/prefix_builder.dart

 // Copyright (c) 2016, 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 fasta.prefix_builder;
 
 import 'builder.dart' show
     Builder,
     LibraryBuilder,
     MemberBuilder;
 
+import '../messages.dart' show
+    warning;
+
 import 'package:kernel/ast.dart' show
     Member;
 
 import '../dill/dill_member_builder.dart' show
     DillMemberBuilder;
 
 import '../errors.dart' show
     internalError;
 
 class PrefixBuilder extends Builder {
   final String name;
 
   final Map<String, Builder> exports;
 
   final LibraryBuilder parent;
 
   PrefixBuilder(this.name, this.exports, LibraryBuilder parent, int charOffset)
       : parent = parent, super(parent, charOffset, parent.fileUri);
 
   Member findTopLevelMember(String name) {
     // TODO(ahe): Move this to KernelPrefixBuilder.
     Builder builder = exports[name];
     if (builder == null) {
-      // TODO(ahe): Report error?
-      print("${this.name} has no member named $name");
+      warning(parent.fileUri, -1,
+          "'${this.name}' has no member named '$name'.");
     }
     if (builder is DillMemberBuilder) {
       return builder.member.isInstanceMember
           ? internalError("Unexpected instance member in export scope")
           : builder.member;
     } else if (builder is MemberBuilder) {
       return builder.target;
     } else {
       return null;
     }
   }
 
   Builder combineAmbiguousImport(String name, Builder other,
       LibraryBuilder library) {
     if (other is PrefixBuilder) {
       /// Handles the case where the same prefix is used for different imports.
       other.exports.forEach((String name, Builder member) {
         Builder existing = exports[name];
         if (existing != null) {
           member = existing.combineAmbiguousImport(name, member, library);
         }
         exports[name] = member;
       });
       return this;
     }
     return super.combineAmbiguousImport(name, other, library);
   }
 }