Move a bunch of src/ files into subdirectories.

test/utils.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.test.utils;
 
 import 'dart:async';
 import 'dart:collection';
 
-import 'package:unittest/src/invoker.dart';
-import 'package:unittest/src/live_test.dart';
-import 'package:unittest/src/load_exception.dart';
-import 'package:unittest/src/remote_exception.dart';
-import 'package:unittest/src/state.dart';
-import 'package:unittest/src/suite.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/load_exception.dart';
+import 'package:unittest/src/util/remote_exception.dart';
 import 'package:unittest/unittest.dart';
 
 // The last state change detected via [expectStates].
 State lastState;
 
 /// Asserts that exactly [states] will be emitted via [liveTest.onStateChange].
 ///
 /// The most recent emitted state is stored in [_lastState].
 void expectStates(LiveTest liveTest, Iterable<State> statesIter) {
   var states = new Queue.from(statesIter);
@@ skipping 206 matching lines @@
     });
   });
 
   return liveTest.run().then((_) {
     expectTestPassed(liveTest);
     // Ensure that the outer test doesn't complete until the inner future
     // completes.
     return future;
   });
 }