Fix for extra space preceding the 'on' keyword in a catch clause (dartbug.com/15454).

pkg/analyzer/lib/src/services/formatter_impl.dart

 // Copyright (c) 2013, 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 formatter_impl;
 
 import 'dart:math';
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/src/generated/java_core.dart' show CharSequence;
@@ skipping 448 matching lines @@
 
   visitCascadeExpression(CascadeExpression node) {
     visit(node.target);
     indent(2);
     visitNodes(node.cascadeSections);
     unindent(2);
   }
 
   visitCatchClause(CatchClause node) {
 
-    token(node.onKeyword, precededBy: space, followedBy: space);
+    token(node.onKeyword, followedBy: space);
     visit(node.exceptionType);
 
     if (node.catchKeyword != null) {
       if (node.exceptionType != null) {
         space();
       }
       token(node.catchKeyword);
       space();
       token(node.leftParenthesis);
       visit(node.exceptionParameter);
@@ skipping 1085 matching lines @@
     var lastLine =
         lineInfo.getLocation(lastOffset).lineNumber;
     var currentLine =
         lineInfo.getLocation(currentOffset).lineNumber;
     return currentLine - lastLine;
   }
 
   String toString() => writer.toString();
 
 }