Fix hints in the analyzer package.

pkg/analyzer/lib/file_system/memory_file_system.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.
 
 library memory_file_system;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/engine.dart' show TimestampedData;
@@ skipping 294 matching lines @@
   @override
   int get hashCode => id;
 
   @override
   bool get isInSystemLibrary => uriKind == UriKind.DART_URI;
 
   @override
   int get modificationStamp {
     try {
       return file.modificationStamp;
-    } on FileSystemException catch (e) {
+    } on FileSystemException {
       return -1;
     }
   }
 
   @override
   String get shortName => file.shortName;
 
   @override
   UriKind get uriKind {
     String scheme = uri.scheme;
@@ skipping 135 matching lines @@
   bool operator ==(other) {
     if (runtimeType != other.runtimeType) {
       return false;
     }
     return path == other.path;
   }
 
   @override
   String toString() => path;
 }