Ensure locations are always provided, but don't store them yet.

pkg/front_end/lib/src/fasta/builder/metadata_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.metadata_builder;
 
 import 'builder.dart' show
     Builder,
     TypeBuilder;
 
 import 'constructor_reference_builder.dart' show
     ConstructorReferenceBuilder;
 
 abstract class MetadataBuilder<T extends TypeBuilder> extends Builder {
-  MetadataBuilder();
+  MetadataBuilder(Builder parent, int charOffset)
+      : super(parent, -1, parent.fileUri);
 
   factory MetadataBuilder.fromConstructor(
-      ConstructorReferenceBuilder constructorReference, List arguments) {
-    return new ConstructorMetadataBuilder(constructorReference, arguments);
+      ConstructorReferenceBuilder constructorReference, List arguments,
+      Builder parent, int charOffset) {
+    return new ConstructorMetadataBuilder(constructorReference, arguments,
+        parent, charOffset);
   }
 
-  factory MetadataBuilder.fromExpression(String expression, String postfix) {
-    return new ExpressionMetadataBuilder(expression, postfix);
+  factory MetadataBuilder.fromExpression(String expression, String postfix,
+      Builder parent, int charOffset) {
+    return new ExpressionMetadataBuilder(
+        expression, postfix, parent, charOffset);
   }
 }
 
 class ConstructorMetadataBuilder<T extends TypeBuilder>
     extends MetadataBuilder<T> {
   final ConstructorReferenceBuilder constructorReference;
 
   final List arguments;
 
-  ConstructorMetadataBuilder(this.constructorReference, this.arguments);
+  ConstructorMetadataBuilder(this.constructorReference, this.arguments,
+      Builder parent, int charOffset)
+      : super(parent, charOffset);
 }
 
 /// Expression metadata (without arguments).
 ///
 /// Matches this grammar rule:
 ///
 ///    '@' qualified (‘.’ identifier)?
 class ExpressionMetadataBuilder<T extends TypeBuilder>
     extends MetadataBuilder<T> {
   final String qualified;
 
   final String identifier;
 
-  ExpressionMetadataBuilder(this.qualified, this.identifier);
+  ExpressionMetadataBuilder(this.qualified, this.identifier, Builder parent,
+      int charOffset)
+      : super(parent, charOffset);
 }