[WebPayments] Implement state transitions in desktop WebPayments dialog.

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

Index: chrome/browser/ui/views/payments/payment_sheet_state_observer.h
diff --git a/chrome/browser/ui/views/payments/payment_sheet_state_observer.h b/chrome/browser/ui/views/payments/payment_sheet_state_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..4d2ca6e48184d853eb03d7fe6896ed7512effe54
--- /dev/null
+++ b/chrome/browser/ui/views/payments/payment_sheet_state_observer.h
@@ -0,0 +1,20 @@
+// 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_SHEET_STATE_OBSERVER_H_
+#define CHROME_BROWSER_UI_VIEWS_PAYMENTS_PAYMENT_SHEET_STATE_OBSERVER_H_
+
+namespace payments {
+
+class PaymentSheetStateObserver {
+ public:
+  virtual void OnOrderSummaryClicked() {}
+
+protected:
+  virtual ~PaymentSheetStateObserver() {}
+};
+
+}  // namespace payments
+
+#endif  // CHROME_BROWSER_UI_VIEWS_PAYMENTS_PAYMENT_SHEET_STATE_OBSERVER_H_