Use an MutationObserver to check when a password form disappears after XHR

third_party/WebKit/public/web/modules/password_manager/WebFormElementObserverCallback.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef WebFormElementObserverCallback_h
+#define WebFormElementObserverCallback_h
+
+namespace blink {
+
+class WebFormElementObserverCallback {
+ public:
+  virtual ~WebFormElementObserverCallback() {}
+
+  // Invoked when the observed element was either removed from the DOM, it's
+  // action attribute changed, or it's computed style changed to display: none.
+  virtual void ElementWasHiddenOrRemoved() = 0;
+};
+
+}  // namespace blink
+
+#endif  // WebFormElementObserverCallback_h