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

third_party/WebKit/Source/web/WebFormElementObserverImpl.h

Index: third_party/WebKit/Source/web/WebFormElementObserverImpl.h
diff --git a/third_party/WebKit/Source/web/WebFormElementObserverImpl.h b/third_party/WebKit/Source/web/WebFormElementObserverImpl.h
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+// 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 WebFormElementObserverImpl_h
+#define WebFormElementObserverImpl_h
+
+#include "platform/heap/HeapAllocator.h"
+#include "platform/heap/Member.h"
+#include "platform/heap/SelfKeepAlive.h"
+#include "platform/wtf/Compiler.h"
+#include "public/web/modules/password_manager/WebFormElementObserver.h"
+#include "web/WebExport.h"
+
+namespace blink {
+
+class HTMLElement;
+class WebFormElementObserverCallback;
+
+class WEB_EXPORT WebFormElementObserverImpl final
+    : public GarbageCollectedFinalized<WebFormElementObserverImpl>,
+      NON_EXPORTED_BASE(public WebFormElementObserver) {
+  WTF_MAKE_NONCOPYABLE(WebFormElementObserverImpl);
+
+ public:
+  WebFormElementObserverImpl(HTMLElement&,
+                             std::unique_ptr<WebFormElementObserverCallback>);
+  ~WebFormElementObserverImpl() override;
+
+  // WebFormElementObserver implementation.
+  void Disconnect() override;
+
+  DECLARE_VIRTUAL_TRACE();
+
+ private:
+  class ObserverCallback;
+
+  Member<ObserverCallback> mutation_callback_;
+
+  // WebFormElementObserverImpl must remain alive until Disconnect() is called.
+  SelfKeepAlive<WebFormElementObserverImpl> self_keep_alive_;
+};
+
+}  // namespace blink
+
+#endif  // WebFormElementObserverImpl_h