[sessions] Introduce iOS implementation of LiveTab interface

This CL introduces IOSLiveTab, an iOS-specific implementation of the LiveTab
interface that is backed by WebState (the iOS analogue of WebContents).

BUG=371476

Review URL: https://codereview.chromium.org/1372103002

Cr-Commit-Position: refs/heads/master@{#351100}

components/sessions.gypi

@@ -147,6 +147,8 @@
           'sources': [
             '<@(sessions_core_sources)',
 
+            'sessions/ios/ios_live_tab.cc',
+            'sessions/ios/ios_live_tab.h',
             'sessions/ios/ios_serialized_navigation_builder.cc',
             'sessions/ios/ios_serialized_navigation_builder.h',
             'sessions/ios/ios_serialized_navigation_driver.cc',

components/sessions/BUILD.gn

@@ -41,6 +41,8 @@ if (!is_ios) {
 } else {
   source_set("sessions") {
     sources = [
+      "ios/ios_live_tab.cc",
+      "ios/ios_live_tab.h",
       "ios/ios_serialized_navigation_builder.cc",
       "ios/ios_serialized_navigation_builder.h",
       "ios/ios_serialized_navigation_driver.cc",

components/sessions/ios/ios_live_tab.cc

+// Copyright 2015 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 "components/sessions/ios/ios_live_tab.h"
+#include "ios/web/public/navigation_manager.h"
+
+namespace {
+const char kIOSLiveTabWebStateUserDataKey[] = "ios_live_tab";
+}
+
+namespace sessions {
+
+std::string IOSLiveTab::user_agent_override_;
+
+// static
+IOSLiveTab* IOSLiveTab::GetForWebState(web::WebState* web_state) {
+  if (!web_state->GetUserData(kIOSLiveTabWebStateUserDataKey)) {
+    web_state->SetUserData(kIOSLiveTabWebStateUserDataKey,
+                           new IOSLiveTab(web_state));
+  }
+
+  return static_cast<IOSLiveTab*>(
+      web_state->GetUserData(kIOSLiveTabWebStateUserDataKey));
+}
+
+IOSLiveTab::IOSLiveTab(web::WebState* web_state) : web_state_(web_state) {}
+
+IOSLiveTab::~IOSLiveTab() {}
+
+int IOSLiveTab::GetCurrentEntryIndex() {
+  return navigation_manager()->GetCurrentEntryIndex();
+}
+
+int IOSLiveTab::GetPendingEntryIndex() {
+  return navigation_manager()->GetPendingItemIndex();
+}
+
+sessions::SerializedNavigationEntry IOSLiveTab::GetEntryAtIndex(int index) {
+  return sessions::IOSSerializedNavigationBuilder::FromNavigationItem(
+      index, *navigation_manager()->GetItemAtIndex(index));
+}
+
+sessions::SerializedNavigationEntry IOSLiveTab::GetPendingEntry() {
+  return sessions::IOSSerializedNavigationBuilder::FromNavigationItem(
+      GetPendingEntryIndex(), *navigation_manager()->GetPendingItem());
+}
+
+int IOSLiveTab::GetEntryCount() {
+  return navigation_manager()->GetEntryCount();
+}
+
+void IOSLiveTab::LoadIfNecessary() {
+  navigation_manager()->LoadIfNecessary();
+}
+
+const std::string& IOSLiveTab::GetUserAgentOverride() const {
+  // Dynamic user agent overrides are not supported on iOS.
+  return user_agent_override_;
+}
+
+}  // namespace sessions

components/sessions/ios/ios_live_tab.h

+// Copyright 2015 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 COMPONENTS_SESSIONS_IOS_IOS_LIVE_TAB_H_
+#define COMPONENTS_SESSIONS_IOS_IOS_LIVE_TAB_H_
+
+#include "base/basictypes.h"
+#include "base/supports_user_data.h"
+#include "components/sessions/core/live_tab.h"
+#include "components/sessions/ios/ios_serialized_navigation_builder.h"
+#include "ios/web/public/web_state/web_state.h"
+
+namespace content {
+class NavigationManager;
+class NavigationEntry;
+}
+
+namespace sessions {
+
+// An implementation of LiveTab that is backed by web::WebState for use
+// on //ios/web-based platforms.
+class SESSIONS_EXPORT IOSLiveTab : public LiveTab,
+                                   public base::SupportsUserData::Data {
+ public:
+  ~IOSLiveTab() override;
+
+  // Returns the IOSLiveTab associated with |web_state|, creating it if
+  // it has not already been created.
+  static IOSLiveTab* GetForWebState(web::WebState* web_state);
+
+  // LiveTab:
+  int GetCurrentEntryIndex() override;
+  int GetPendingEntryIndex() override;
+  sessions::SerializedNavigationEntry GetEntryAtIndex(int index) override;
+  sessions::SerializedNavigationEntry GetPendingEntry() override;
+  int GetEntryCount() override;
+  void LoadIfNecessary() override;
+  const std::string& GetUserAgentOverride() const override;
+
+  web::WebState* web_state() { return web_state_; }
+  const web::WebState* web_state() const { return web_state_; }
+
+ private:
+  friend class base::SupportsUserData;
+
+  explicit IOSLiveTab(web::WebState* web_state);
+
+  web::NavigationManager* navigation_manager() {
+    return web_state_->GetNavigationManager();
+  }
+
+  web::WebState* web_state_;
+
+  // Needed to return an empty string in GetUserAgentOverride().
+  static std::string user_agent_override_;
+
+  DISALLOW_COPY_AND_ASSIGN(IOSLiveTab);
+};
+
+}  // namespace sessions
+
+#endif  // COMPONENTS_SESSIONS_IOS_IOS_LIVE_TAB_H_