[sessions] Introduce iOS implementation of LiveTab interface

components/sessions/ios/ios_live_tab.h

Index: components/sessions/ios/ios_live_tab.h
diff --git a/components/sessions/ios/ios_live_tab.h b/components/sessions/ios/ios_live_tab.h
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+++ b/components/sessions/ios/ios_live_tab.h
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+// 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_