Prepare for development branch by updating externally-used API.

pkg/front_end/lib/src/fasta/scope.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.scope;
 
 import 'builder/builder.dart' show Builder, TypeVariableBuilder;
 
-import 'errors.dart' show internalError;
+import 'errors.dart' show InputError, internalError;
 
 class MutableScope {
   /// Names declared in this scope.
   Map<String, Builder> local;
 
   /// Setters declared in this scope.
   Map<String, Builder> setters;
 
   /// The scope that this scope is nested within, or `null` if this is the top
   /// level scope.
@@ skipping 140 matching lines @@
   }
 
   Map<String, Builder> get unclaimedForwardDeclarations {
     return forwardDeclaredLabels;
   }
 
   Builder lookupLabel(String name) {
     return (labels == null ? null : labels[name]) ?? parent?.lookupLabel(name);
   }
 
-  // TODO(ahe): Rename to extend or something.
-  void operator []=(String name, Builder member) {
+  InputError declare(
+      String name, Builder builder, int charOffset, Uri fileUri) {

[scheglov, 2017/05/23 16:14:45]

Please document the method and meaning of the parameters.

[ahe, 2017/05/24 10:54:20]

Done.

     if (isModifiable) {
       local[name] = member;
     } else {
       internalError("Can't extend an unmodifiable scope.");
     }
+    return null;

[ahe, 2017/05/23 15:04:24]

Will eventually return an InputError if the name is already used in this scope.

   }
 
   void merge(Scope scope,
       buildAmbiguousBuilder(String name, Builder existing, Builder member)) {
     Map<String, Builder> map = local;
 
     void mergeMember(String name, Builder member) {
       Builder existing = map[name];
       if (existing != null) {
         if (existing != member) {
@@ skipping 100 matching lines @@
 
   String get message => "Access error: '$name'.";
 }
 
 class AmbiguousBuilder extends ProblemBuilder {
   AmbiguousBuilder(String name, Builder builder, int charOffset, Uri fileUri)
       : super(name, builder, charOffset, fileUri);
 
   String get message => "Duplicated named: '$name'.";
 }