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

components/autofill/content/renderer/password_autofill_agent.cc

Index: components/autofill/content/renderer/password_autofill_agent.cc
diff --git a/components/autofill/content/renderer/password_autofill_agent.cc b/components/autofill/content/renderer/password_autofill_agent.cc
index 062823790691580d1b96b309733e65eb693cc7be..a202c8b3b75ea675d03632f579a5db850f1571e3 100644
--- a/components/autofill/content/renderer/password_autofill_agent.cc
+++ b/components/autofill/content/renderer/password_autofill_agent.cc
@@ -44,6 +44,7 @@
 #include "third_party/WebKit/public/web/WebDocument.h"
 #include "third_party/WebKit/public/web/WebElement.h"
 #include "third_party/WebKit/public/web/WebFormElement.h"
+#include "third_party/WebKit/public/web/WebFormElementObserverCallback.h"
 #include "third_party/WebKit/public/web/WebLocalFrame.h"
 #include "third_party/WebKit/public/web/WebNode.h"
 #include "third_party/WebKit/public/web/WebUserGestureIndicator.h"
@@ -618,6 +619,35 @@ bool HasPasswordField(const blink::WebLocalFrame& frame) {
 
 }  // namespace
 
+class PasswordAutofillAgent::FormElementObserver
+    : public blink::WebFormElementObserverCallback {
+ public:
+  explicit FormElementObserver(PasswordAutofillAgent* agent) : agent_(agent) {}
+  ~FormElementObserver() override { Detach(); }
+
+  void Detach() {
+    if (agent_) {
+      DCHECK_EQ(agent_->form_element_observer_, this);
+      agent_->form_element_observer_ = nullptr;
+    }
+    agent_ = nullptr;
+  }
+
+  bool ShouldStopObserving() override {
+    if (!agent_)
+      return true;
+    agent_->OnSameDocumentNavigationCompleted();
+    // The above call will invoke Detach() if the form no longer needs to be
+    // observed.
+    return agent_ == nullptr;
+  }
+
+ private:
+  PasswordAutofillAgent* agent_;
+
+  DISALLOW_COPY_AND_ASSIGN(FormElementObserver);
+};
+
 ////////////////////////////////////////////////////////////////////////////////
 // PasswordAutofillAgent, public:
 
@@ -628,13 +658,16 @@ PasswordAutofillAgent::PasswordAutofillAgent(content::RenderFrame* render_frame)
       was_password_autofilled_(false),
       sent_request_to_store_(false),
       checked_safe_browsing_reputation_(false),
-      binding_(this) {
+      binding_(this),
+      form_element_observer_(nullptr) {
   // PasswordAutofillAgent is guaranteed to outlive |render_frame|.
   render_frame->GetInterfaceRegistry()->AddInterface(
       base::Bind(&PasswordAutofillAgent::BindRequest, base::Unretained(this)));
 }
 
 PasswordAutofillAgent::~PasswordAutofillAgent() {
+  if (form_element_observer_)
+    form_element_observer_->Detach();
 }
 
 void PasswordAutofillAgent::BindRequest(
@@ -1051,10 +1084,28 @@ void PasswordAutofillAgent::OnSameDocumentNavigationCompleted() {
            frame, provisionally_saved_form_.input_element(),
            password_form.action, password_form.origin, password_form.form_data,
            form_predictions_))) {
+    if (!form_element_observer_) {
+      std::unique_ptr<FormElementObserver> observer(
+          new FormElementObserver(this));
+      form_element_observer_ = observer.get();
+      if (provisionally_saved_form_.form_element().IsNull()) {
+        provisionally_saved_form_.input_element()
+            .GetDocument()
+            .ObserveFormElement(provisionally_saved_form_.input_element(),
+                                std::move(observer));
+      } else {
+        provisionally_saved_form_.form_element()
+            .GetDocument()
+            .ObserveFormElement(provisionally_saved_form_.form_element(),
+                                std::move(observer));
+      }
+    }
     return;
   }
 
   GetPasswordManagerDriver()->InPageNavigation(password_form);
+  if (form_element_observer_)
+    form_element_observer_->Detach();
   provisionally_saved_form_.Reset();
 }
 
@@ -1287,6 +1338,8 @@ void PasswordAutofillAgent::WillSubmitForm(const blink::WebFormElement& form) {
     // RenderView to be instantiated (such as redirects to the WebStore)
     // we will never get to finish the load.
     GetPasswordManagerDriver()->PasswordFormSubmitted(*submitted_form);
+    if (form_element_observer_)
+      form_element_observer_->Detach();
     provisionally_saved_form_.Reset();
   } else if (logger) {
     logger->LogMessage(Logger::STRING_FORM_IS_NOT_PASSWORD);
@@ -1334,6 +1387,8 @@ void PasswordAutofillAgent::DidStartProvisionalLoad(
       }
       GetPasswordManagerDriver()->PasswordFormSubmitted(
           provisionally_saved_form_.password_form());
+      if (form_element_observer_)
+        form_element_observer_->Detach();
       provisionally_saved_form_.Reset();
     } else {
       std::vector<std::unique_ptr<PasswordForm>> possible_submitted_forms;
@@ -1615,6 +1670,8 @@ void PasswordAutofillAgent::FrameClosing() {
     password_to_username_.erase(iter.second.password_field);
   }
   web_input_to_password_info_.clear();
+  if (form_element_observer_)
+    form_element_observer_->Detach();
   provisionally_saved_form_.Reset();
   field_value_and_properties_map_.clear();
   sent_request_to_store_ = false;