Display a pause screen in a paused browser.

lib/src/runner.dart

Index: lib/src/runner.dart
diff --git a/lib/src/runner.dart b/lib/src/runner.dart
index 3e2ab47aca656b98c601950377390f20e3fd5cf6..0ca8e67e99191c4c2cb9f0f3ef78c34c7b2d912e 100644
--- a/lib/src/runner.dart
+++ b/lib/src/runner.dart
@@ -238,10 +238,10 @@ class Runner {
               "${suite.platform} and set breakpoints. Once you're finished, "
               "return to this terminal and press Enter."));
 
-      // TODO(nweiz): Display something in the paused browsers indicating that
-      // they're paused.
-
-      await stdinLines.next;
+      await race([
+        suite.environment.displayPause(),
+        cancelableNext(stdinLines)
+      ]);
     } finally {
       _reporter.resume();
     }