Move a bunch of src/ files into subdirectories.

lib/src/util/remote_exception.dart

 // Copyright (c) 2015, 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 unittest.remote_exception;
+library unittest.util.remote_exception;
 
 import 'dart:async';
 import 'dart:isolate';
 
 import 'package:stack_trace/stack_trace.dart';
 
-import 'expect.dart';
+import '../frontend/expect.dart';
 
 /// An exception that was thrown remotely.
 ///
 /// This could be an exception thrown in a different isolate, a different
 /// process, or on an entirely different computer.
 class RemoteException implements Exception {
   /// The original exception's message, if it had one.
   ///
   /// If the original exception was a plain string, this will contain that
   /// string.
@@ skipping 79 matching lines @@
   _RemoteTestFailure(String message, String type, String toString)
       : super._(message, type, toString);
 }
 
 /// A subclass of [RemoteException] that implements [IsolateSpawnException].
 class _RemoteIsolateSpawnException extends RemoteException
     implements IsolateSpawnException {
   _RemoteIsolateSpawnException(String message, String type, String toString)
       : super._(message, type, toString);
 }