[WebPayments] Implement state transitions in desktop WebPayments dialog.

chrome/browser/ui/views/payments/order_summary_state.cc

+// 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.
+
+#include "chrome/browser/ui/views/payments/order_summary_state.h"
+
+#include "base/observer_list.h"
+#include "base/strings/utf_string_conversions.h"
+#include "chrome/grit/generated_resources.h"
+#include "ui/base/l10n/l10n_util.h"
+#include "ui/views/controls/button/md_text_button.h"
+#include "ui/views/controls/label.h"
+#include "ui/views/layout/grid_layout.h"
+
+namespace {
+
+// The tag for the button that navigates back to the payment sheet.
+constexpr int kBackButtonTag = 0;
+
+}  // namespace
+
+namespace payments {
+
+OrderSummaryState::OrderSummaryState() {}
+
+OrderSummaryState::~OrderSummaryState() {}
+
+views::View* OrderSummaryState::CreateView() {
+  views::View* view = new views::View();
+
+  views::GridLayout* layout = new views::GridLayout(view);
+  view->SetLayoutManager(layout);
+  views::ColumnSet* columns = layout->AddColumnSet(0);
+  columns->AddColumn(views::GridLayout::TRAILING, views::GridLayout::CENTER,
+                     0, views::GridLayout::USE_PREF, 0, 0);
+
+  layout->StartRow(0, 0);
+  layout->AddView(new views::Label(
+      l10n_util::GetStringUTF16(IDS_PAYMENT_REQUEST_ORDER_SUMMARY_TITLE)));
+
+  layout->StartRow(0, 0);
+  views::LabelButton* back_button =
+      views::MdTextButton::CreateSecondaryUiBlueButton(
+          this, base::ASCIIToUTF16("Back"));
+  back_button->set_tag(kBackButtonTag);
+  layout->AddView(back_button);
+
+  return view;
+}
+
+void OrderSummaryState::AddObserver(OrderSummaryStateObserver* observer) {
+  observers_.AddObserver(observer);
+}
+
+void OrderSummaryState::RemoveObserver(OrderSummaryStateObserver* observer) {
+  observers_.RemoveObserver(observer);
+}
+
+void OrderSummaryState::ButtonPressed(
+    views::Button* sender, const ui::Event& event) {
+  DCHECK_EQ(kBackButtonTag, sender->tag());
+  for (auto& observer : observers_) {
+    observer.OnBackClicked();
+  }
+
+}
+
+}  // namespace payments