Factor out some common logic from the launchers.

test/runner/browser/chrome_test.dart

Index: test/runner/browser/chrome_test.dart
diff --git a/test/runner/browser/chrome_test.dart b/test/runner/browser/chrome_test.dart
index 1886111d26e79ff41b3d0f26d69814385a7ce641..deb80a120acc7a930bd98769fce6b71dba7eed7a 100644
--- a/test/runner/browser/chrome_test.dart
+++ b/test/runner/browser/chrome_test.dart
@@ -145,6 +145,6 @@ webSocket.addEventListener("open", function() {
     var chrome = new Chrome("http://dart-lang.org",
         executable: "_does_not_exist");
     expect(chrome.onExit, throwsA(isApplicationException(startsWith(
-        "Failed to start Chrome: $noSuchFileMessage"))));
+        "Failed to run Chrome: $noSuchFileMessage"))));
   });
 }