Focus first invalid field of payment request editor

chrome/browser/ui/views/payments/validation_delegate.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 CHROME_BROWSER_UI_VIEWS_PAYMENTS_VALIDATION_DELEGATE_H_
 #define CHROME_BROWSER_UI_VIEWS_PAYMENTS_VALIDATION_DELEGATE_H_
 
 namespace views {
 class Combobox;
 class Textfield;
 }  // namespace views
 
 namespace payments {
 
 class ValidationDelegate {
  public:
   virtual ~ValidationDelegate() {}
 
-  // Only the delegate knows how to validate the textfield.
-  virtual bool ValidateTextfield(views::Textfield* textfield) = 0;
+  // Only the delegate knows how to validate the input fields.
+  virtual bool IsValidTextfield(views::Textfield* textfield) = 0;
+  virtual bool IsValidCombobox(views::Combobox* combobox) = 0;
 
-  virtual bool ValidateCombobox(views::Combobox* combobox) = 0;
+  // Notifications to let delegate react to input field changes and also let
+  // caller know if the new values are valid.
+  virtual bool TextfieldValueChanged(views::Textfield* textfield) = 0;
+  virtual bool ComboboxValueChanged(views::Combobox* combobox) = 0;
+
+  // Lets the delegate know that the model of the combobox has changed, e.g.,
+  // when it gets filled asynchronously as for the state field.
   virtual void ComboboxModelChanged(views::Combobox* combobox) = 0;
 };
 
 }  // namespace payments
 
 #endif  // CHROME_BROWSER_UI_VIEWS_PAYMENTS_VALIDATION_DELEGATE_H_