[Payments] Add the pay button, and control its enabled state

chrome/browser/ui/views/payments/payment_request_dialog_view.h

 // Copyright 2016 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_PAYMENT_REQUEST_DIALOG_VIEW_H_
 #define CHROME_BROWSER_UI_VIEWS_PAYMENTS_PAYMENT_REQUEST_DIALOG_VIEW_H_
 
 #include <map>
 #include <memory>
 
@@ skipping 43 matching lines @@
   ui::ModalType GetModalType() const override;
 
   // views::DialogDelegate
   bool Cancel() override;
   bool ShouldShowCloseButton() const override;
   int GetDialogButtons() const override;
 
   // payments::PaymentRequestDialog
   void ShowDialog() override;
   void CloseDialog() override;
+  void UpdatePayButtonState(bool enabled) override;
 
   void GoBack();
   void ShowOrderSummary();
   void ShowShippingListSheet();
   void ShowPaymentMethodSheet();
   void ShowCreditCardEditor();
 
   ViewStack* view_stack_for_testing() { return &view_stack_; }
 
  private:
   void ShowInitialPaymentSheet();
 
   // views::View
   gfx::Size GetPreferredSize() const override;
   void ViewHierarchyChanged(
       const ViewHierarchyChangedDetails& details) override;
 
   // Non-owned reference to the PaymentRequest that initiated this dialog. Since
   // the PaymentRequest object always outlives this one, the pointer should
   // always be valid even though there is no direct ownership relationship
   // between the two.
   PaymentRequest* request_;
   ControllerMap controller_map_;
   ViewStack view_stack_;
 
+  // Used to lookup the payment sheet view controller. Weak reference that is
+  // nullified when the view is removed from the hierarchy.
+  views::View* payment_sheet_view_;
+
   // May be null.
   ObserverForTest* observer_for_testing_;
 
   DISALLOW_COPY_AND_ASSIGN(PaymentRequestDialogView);
 };
 
 }  // namespace payments
 
 #endif  // CHROME_BROWSER_UI_VIEWS_PAYMENTS_PAYMENT_REQUEST_DIALOG_VIEW_H_