Display a pause screen in a paused browser.

lib/src/runner/environment.dart

Index: lib/src/runner/environment.dart
diff --git a/lib/src/runner/environment.dart b/lib/src/runner/environment.dart
index 5f2b9467ef59f47f65d5307f357fa235d840d900..14ad720b2edd3935977417c87ac7e93137ee630c 100644
--- a/lib/src/runner/environment.dart
+++ b/lib/src/runner/environment.dart
@@ -4,7 +4,15 @@
 
 library test.runner.environment;
 
+import '../util/cancelable_future.dart';
+
 /// The abstract class of environments in which test suites are
 /// loaded—specifically, browsers and the Dart VM.
 abstract class Environment {
+  /// Displays information indicating that the test runner is paused.
+  ///
+  /// The returned future will complete when the user takes action within the
+  /// environment that should unpause the runner. If the runner is unpaused
+  /// elsewhere, the future should be canceled.
+  CancelableFuture displayPause();
 }