[kernel] Make fasta call a new constructor on FallThroughError

runtime/lib/errors_patch.dart

 // Copyright (c) 2012, 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.
 
 @patch
 class Error {
   @patch
   static String _objectToString(Object object) {
     return Object._toString(object);
   }
@@ skipping 95 matching lines @@
 
   // Fields _url, _line, and _column are only used for debugging purposes.
   final String _url;
   final int _line;
   final int _column;
   final String _errorMsg;
 }
 
 @patch
 class FallThroughError {
-  FallThroughError._create(this._url, this._line);
+  @patch
+  FallThroughError._create(String url, int line)
+      : _url = url,
+        _line = line;
 
   static _throwNew(int case_clause_pos) native "FallThroughError_throwNew";
 
   @patch
   String toString() {
     return "'$_url': Switch case fall-through at line $_line.";
   }
 
   // These new fields cannot be declared final, because a constructor exists
   // in the original version of this patched class.
@@ skipping 302 matching lines @@
   _DuplicatedFieldInitializerError(this._name);
 
   toString() => "Error: field '$_name' is already initialized.";
 }
 
 @patch
 class _ConstantExpressionError {
   @patch
   _throw(error) => throw error;
 }