Factor out some common logic from the launchers.

test/runner/browser/safari_test.dart

Index: test/runner/browser/safari_test.dart
diff --git a/test/runner/browser/safari_test.dart b/test/runner/browser/safari_test.dart
index e31284e5ba69dd0266b6bdab73086818ac3929be..254a0fc865ae569dd296daec54c554f851d0ef8d 100644
--- a/test/runner/browser/safari_test.dart
+++ b/test/runner/browser/safari_test.dart
@@ -142,6 +142,6 @@ webSocket.addEventListener("open", function() {
     var safari = new Safari("http://dart-lang.org",
         executable: "_does_not_exist");
     expect(safari.onExit, throwsA(isApplicationException(startsWith(
-        "Failed to start Safari: $noSuchFileMessage"))));
+        "Failed to run Safari: $noSuchFileMessage"))));
   });
 }