dart2js: Fix hints in code base.

pkg/compiler/lib/src/helpers/trace.dart

 // Copyright (c) 2014, 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.
 
 part of dart2js.helpers;
 
 /// Function signature for [trace].
 typedef void Trace(String message,
                    {bool condition(String stackTrace),
                     int limit,
@@ skipping 137 matching lines @@
         int lastColon = line.lastIndexOf(':', rightParenPos);
         int nextToLastColon = line.lastIndexOf(':', lastColon-1);
 
         String lineNo;
         String columnNo;
         if (nextToLastColon != -1) {
           lineNo = line.substring(nextToLastColon+1, lastColon);
           columnNo = line.substring(lastColon+1, rightParenPos);
           try {
             int.parse(lineNo);
-          } on FormatException catch (e) {
+          } on FormatException {
             lineNo = columnNo;
             columnNo = '';
             nextToLastColon = lastColon;
           }
         } else {
           lineNo = line.substring(lastColon+1, rightParenPos);
           columnNo = '';
           nextToLastColon = lastColon;
         }
 
@@ skipping 161 matching lines @@
   }
   for (int index = text.length ; index < intendedLength ; index ++) {
     int dotsIndex = index % dotsLength;
     sb.write(dots.substring(dotsIndex, dotsIndex + 1));
   }
   if (padLeft) {
     sb.write(text);
   }
   return sb.toString();
 }