[WebPayments] Implement state transitions in desktop WebPayments dialog.

chrome/browser/payments/ui/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 "base/observer_list.h"
+#include "base/strings/utf_string_conversions.h"
+#include "chrome/browser/payments/ui/order_summary_state.h"
+#include "ui/views/controls/button/md_text_button.h"
+#include "ui/views/controls/label.h"
+#include "ui/views/layout/grid_layout.h"
+
+namespace payments {
+
+const int kBackButtonTag = 0;
+
+OrderSummaryState::OrderSummaryState()
+  : view_(nullptr) {}
+
+OrderSummaryState::~OrderSummaryState() {}
+
+views::View* OrderSummaryState::GetView() {
+  if (!view_) {
+    view_ = new views::View();
+    view_->SetSize(gfx::Size(300, 300));
+
+    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(base::ASCIIToUTF16("Order Summary")));
+
+    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(Observer* observer) {
+  observers_.AddObserver(observer);
+}
+
+void OrderSummaryState::RemoveObserver(Observer* observer) {
+  observers_.RemoveObserver(observer);
+}
+
+void OrderSummaryState::ButtonPressed(
+    views::Button* sender, const ui::Event& event) {
+  if (!interactable())
+    return;
+
+  if (sender->tag() == kBackButtonTag) {
+    for (auto& observer : observers_) {
+      observer.OnBackClicked();
+    }
+  }
+}
+
+}  // namespace payments