Make AstFactory.variableDeclaration(charOffset) a required parameter.

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

 // Copyright (c) 2017, 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.
 
 import 'package:kernel/ast.dart';
 
 /// An abstract class containing factory methods that create AST objects.
 ///
 /// Itended for use by [BodyBuilder] so that it can create either analyzer or
 /// kernel ASTs depending on which concrete factory it is connected to.
@@ skipping 43 matching lines @@
 
   /// Creates a variable declaration statement declaring one variable.
   ///
   /// TODO(paulberry): analyzer makes a distinction between a single variable
   /// declaration and a variable declaration statement (which can contain
   /// multiple variable declarations).  Currently this API only makes sense for
   /// kernel, which desugars each variable declaration to its own statement.
   ///
   /// If the variable declaration did not have an explicitly declared type,
   /// [type] should be `null`.
-  VariableDeclaration variableDeclaration(String name,
+  VariableDeclaration variableDeclaration(String name, int charOffset,
       {DartType type,
       Expression initializer,
-      int charOffset = TreeNode.noOffset,
       int equalsCharOffset = TreeNode.noOffset,
       bool isFinal: false,
       bool isConst: false});
 }