Unify dart:async and pub/io.dart TimeoutException classes.

sdk/lib/_internal/pub/lib/src/dart.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.
 
 /// A library for compiling Dart code and manipulating analyzer parse trees.
 library pub.dart;
 
-import 'dart:async' hide TimeoutException;
+import 'dart:async';
 import 'dart:isolate';
 
 import 'package:analyzer/analyzer.dart';
 import 'package:path/path.dart' as path;
 import 'package:stack_trace/stack_trace.dart';
 import '../../../compiler/compiler.dart' as compiler;
 import '../../../compiler/implementation/source_file_provider.dart'
     show FormattingDiagnosticHandler, CompilerSourceFileProvider;
 import '../../../compiler/implementation/filenames.dart'
     show appendSlash;
@@ skipping 162 matching lines @@
   }
 
   String toString() => "$message\n$stackTrace";
 }
 
 /// An exception thrown when dart2js generates compiler errors.
 class CompilerException extends ApplicationException {
   CompilerException(String entrypoint)
       : super('Failed to compile "$entrypoint".');
 }