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

components/autofill/content/renderer/password_autofill_agent.h

Index: components/autofill/content/renderer/password_autofill_agent.h
diff --git a/components/autofill/content/renderer/password_autofill_agent.h b/components/autofill/content/renderer/password_autofill_agent.h
index b8f80e7f3807e64e90c32cc3fe552f6ac1fa63d0..f0ae52c68290a1055bed12ffdd5f48e75cdca6ef 100644
--- a/components/autofill/content/renderer/password_autofill_agent.h
+++ b/components/autofill/content/renderer/password_autofill_agent.h
@@ -147,6 +147,8 @@ class PasswordAutofillAgent : public content::RenderFrameObserver,
       const blink::WebSecurityOrigin& origin);
 
  private:
+  class FormElementObserver;
+
   // Ways to restrict which passwords are saved in ProvisionallySavePassword.
   enum ProvisionallySaveRestriction {
     RESTRICTION_NONE,
@@ -258,7 +260,8 @@ class PasswordAutofillAgent : public content::RenderFrameObserver,
                                  ProvisionallySaveRestriction restriction);
 
   // Helper function called when same-document navigation completed
-  void OnSameDocumentNavigationCompleted(bool is_inpage_navigation);
+  void OnSameDocumentNavigationCompleted(
+      PasswordForm::SubmissionIndicatorEvent event);
 
   const mojom::AutofillDriverPtr& GetAutofillDriver();
 
@@ -308,6 +311,8 @@ class PasswordAutofillAgent : public content::RenderFrameObserver,
 
   mojo::Binding<mojom::PasswordAutofillAgent> binding_;
 
+  FormElementObserver* form_element_observer_;  // Weak reference.
+
   DISALLOW_COPY_AND_ASSIGN(PasswordAutofillAgent);
 };