[WebPayments] Implement state transitions in desktop WebPayments dialog.

chrome/browser/ui/views/payments/view_stack_state.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_VIEW_STACK_STATE_H_
+#define CHROME_BROWSER_UI_VIEWS_PAYMENTS_VIEW_STACK_STATE_H_
+
+#include <memory>
+
+#include "base/macros.h"
+
+namespace views {
+class View;
+}
+
+// Base class for the ViewStack states. Each state represents a view that can be
+// added to the ViewStack and animated by it.
+class ViewStackState {
+ public:
+  ViewStackState();
+  virtual ~ViewStackState();
+
+  // Create the view associated with this state if needed and return it. This
+  // object owns the view and has called set_owned_by_client() on it.
+  views::View* GetView();
+
+ protected:
+  // Create the view associated with this state. Subclasses should override this
+  // to create the view they represent. This is called by GetView(), which calls
+  // set_owned_by_client() so CreateView() doesn't have to do anything about the
+  // ownership of the return view.
+  virtual views::View* CreateView() = 0;
+
+ private:
+  std::unique_ptr<views::View> view_;
+
+  DISALLOW_COPY_AND_ASSIGN(ViewStackState);
+};
+
+#endif  // CHROME_BROWSER_UI_VIEWS_PAYMENTS_VIEW_STACK_STATE_H_