Add a --pause-after-load flag for debugging.

lib/src/runner/reporter.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 test.runner.reporter;
+
+/// An interface for classes that watch the progress of an Engine and report it
+/// to the user.
+///
+/// A reporter should subscribe to the Engine's events as soon as it's created.
+abstract class Reporter {
+  /// Pauses the reporter's output.
+  ///
+  /// Subclasses should buffer any events from the engine while they're paused.
+  /// They should also ensure that this does nothing if the reporter is already
+  /// paused.
+  void pause();
+
+  /// Resumes the reporter's output after being [paused].
+  ///
+  /// Subclasses should ensure that this does nothing if the reporter isn't
+  /// paused.
+  void resume();
+
+  /// Cancels the reporter's output.
+  void cancel();
+}