Added flags & experiments for the fullscreen notifications feature.

BUG=648388

Review-Url: https://codereview.chromium.org/2377283008
Cr-Commit-Position: refs/heads/master@{#424179}
diff --git a/chrome/browser/notifications/web_notification_delegate.h b/chrome/browser/notifications/web_notification_delegate.h
index 93c46ab..78aaa6b1c 100644
--- a/chrome/browser/notifications/web_notification_delegate.h
+++ b/chrome/browser/notifications/web_notification_delegate.h
@@ -7,6 +7,7 @@
 
 #include <string>
 
+#include "base/feature_list.h"
 #include "base/macros.h"
 #include "chrome/browser/notifications/notification_delegate.h"
 #include "url/gurl.h"
@@ -15,6 +16,12 @@
 class BrowserContext;
 }
 
+namespace features {
+
+extern const base::Feature kAllowFullscreenWebNotificationsFeature;
+
+} // namespace features
+
 // Base class for the PersistentNotificationDelegate and the
 // NotificationObjectProxy. All common functionality for displaying web
 // notifications is found here.