Move public methods of RenderFrameObserver to public section of PasswordAutofillAgent

See an explanation at https://chromium-review.googlesource.com/c/chromium/src/+/1306497/6/chrome/renderer/autofill/password_autofill_agent_browsertest.cc#3682.
Short version of the explanation: it's a bad practice to use public inheritance and put public methods of the base class to the private section of the derived class.

Bug: 898109
Change-Id: Ie9ceed5e860593490ec39788c6a0c353bfdd6947
Reviewed-on: https://chromium-review.googlesource.com/c/1347361Reviewed-by: Roger McFarlane <rogerm@chromium.org>
Reviewed-by: Vadym Doroshenko <dvadym@chromium.org>
Commit-Queue: Uladzimir Miniailau <miniailau@google.com>
Cr-Commit-Position: refs/heads/master@{#610460}

components/autofill/content/renderer/password_autofill_agent.h

@@ -190,6 +190,16 @@ class PasswordAutofillAgent : public content::RenderFrameObserver,
   // unique origins aren't allowed access.
   virtual bool FrameCanAccessPasswordManager();
 
+  // RenderFrameObserver:
+  void DidFinishDocumentLoad() override;
+  void DidFinishLoad() override;
+  void DidStartProvisionalLoad(blink::WebDocumentLoader* document_loader,
+                               bool is_content_initiated) override;
+  void WillCommitProvisionalLoad() override;
+  void DidCommitProvisionalLoad(bool is_same_document_navigation,
+                                ui::PageTransition transition) override;
+  void OnDestruct() override;
+
  private:
   // Ways to restrict which passwords are saved in ProvisionallySavePassword.
   enum ProvisionallySaveRestriction {
@@ -259,16 +269,6 @@ class PasswordAutofillAgent : public content::RenderFrameObserver,
     DISALLOW_COPY_AND_ASSIGN(PasswordValueGatekeeper);
   };
 
-  // RenderFrameObserver:
-  void DidFinishDocumentLoad() override;
-  void DidFinishLoad() override;
-  void DidStartProvisionalLoad(blink::WebDocumentLoader* document_loader,
-                               bool is_content_initiated) override;
-  void WillCommitProvisionalLoad() override;
-  void DidCommitProvisionalLoad(bool is_same_document_navigation,
-                                ui::PageTransition transition) override;
-  void OnDestruct() override;
-
   // Scans the given frame for password forms and sends them up to the browser.
   // If |only_visible| is true, only forms visible in the layout are sent.
   void SendPasswordForms(bool only_visible);