Make AstFactory.variableDeclaration(charOffset) a required parameter.

pkg/front_end/lib/src/fasta/kernel/kernel_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';
 
 import '../builder/ast_factory.dart';
 import 'kernel_shadow_ast.dart';
 
 /// Concrete implementation of [builder.AstFactory] for building a kernel AST.
@@ skipping 20 matching lines @@
   KernelNullLiteral nullLiteral(int charOffset) {
     return new KernelNullLiteral()..fileOffset = charOffset;
   }
 
   @override
   KernelReturnStatement returnStatement(Expression expression, int charOffset) {
     return new KernelReturnStatement(expression)..fileOffset = charOffset;
   }
 
   @override
-  KernelVariableDeclaration variableDeclaration(String name,
+  KernelVariableDeclaration variableDeclaration(String name, int charOffset,
       {DartType type,
       Expression initializer,
-      int charOffset = TreeNode.noOffset,
       int equalsCharOffset = TreeNode.noOffset,
       bool isFinal: false,
       bool isConst: false}) {
     return new KernelVariableDeclaration(name,
         type: type,
         initializer: initializer,
         isFinal: isFinal,
         isConst: isConst)
       ..fileOffset = charOffset
       ..fileEqualsOffset = equalsCharOffset;
   }
 }