Introduce BrowserList and Browser classes for iOS.

ios/clean/chrome/browser/model/browser_list.h

Index: ios/clean/chrome/browser/model/browser_list.h
diff --git a/ios/clean/chrome/browser/model/browser_list.h b/ios/clean/chrome/browser/model/browser_list.h
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+++ b/ios/clean/chrome/browser/model/browser_list.h
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+// Copyright 2017 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 IOS_CLEAN_CHROME_BROWSER_MODEL_BROWSER_LIST_H_
+#define IOS_CLEAN_CHROME_BROWSER_MODEL_BROWSER_LIST_H_
+
+#include <vector>
+
+#include "base/macros.h"
+#include "base/supports_user_data.h"
+#include "ios/clean/chrome/browser/model/browser.h"
+
+namespace ios {
+class ChromeBrowserState;
+}
+
+// BrowserList attaches Browsers instance to a ChromeBrowserState.
+class BrowserList : public base::SupportsUserData::Data {
+ public:
+  explicit BrowserList(ios::ChromeBrowserState* browser_state);
+  ~BrowserList() override;
+
+  static BrowserList* FromBrowserState(ios::ChromeBrowserState* browser_state);
+
+  // Returns the number of open Browsers.
+  int GetBrowserCount() const;
+
+  // Returns whether the specified index is valid.
+  int ContainsIndex(int index) const;
+
+  // Returns the Browser at the specified index.
+  Browser* GetBrowserAtIndex(int index) const;
+
+  // Creates and returns a new Browser instance.
+  Browser* CreateNewBrowser();
+
+  // Closes the Browser at the specified index.
+  void CloseBrowserAtIndex(int index);
+
+ private:
+  std::vector<std::unique_ptr<Browser>> browsers_;
+  ios::ChromeBrowserState* browser_state_;
+
+  DISALLOW_COPY_AND_ASSIGN(BrowserList);
+};
+
+#endif  // IOS_CLEAN_CHROME_BROWSER_MODEL_BROWSER_LIST_H_