Move a bunch of src/ files into subdirectories.

test/vm_listener_test.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.
 
 import 'dart:async';
 import 'dart:isolate';
 
-import 'package:unittest/src/invoker.dart';
-import 'package:unittest/src/io.dart';
-import 'package:unittest/src/isolate_test.dart';
-import 'package:unittest/src/live_test.dart';
-import 'package:unittest/src/remote_exception.dart';
-import 'package:unittest/src/state.dart';
-import 'package:unittest/src/suite.dart';
-import 'package:unittest/src/vm_listener.dart';
+import 'package:unittest/src/backend/invoker.dart';
+import 'package:unittest/src/backend/live_test.dart';
+import 'package:unittest/src/backend/state.dart';
+import 'package:unittest/src/backend/suite.dart';
+import 'package:unittest/src/runner/isolate_test.dart';
+import 'package:unittest/src/runner/vm_listener.dart';
+import 'package:unittest/src/util/io.dart';
+import 'package:unittest/src/util/remote_exception.dart';
 import 'package:unittest/unittest.dart';
 
 import 'utils.dart';
 
 /// An isolate that's been spun up for the current test.
 ///
 /// This is tracked so that it can be killed once the test is done.
 Isolate _isolate;
 
 /// A live test that's running for the current test.
@@ skipping 343 matching lines @@
   VmListener.start(sendPort, () => () {
     test("multiple errors", () {
       Invoker.current.addOutstandingCallback();
       new Future(() => throw "one");
       new Future(() => throw "two");
       new Future(() => throw "three");
       new Future(() => throw "four");
     });
   });
 }