Introduce BrowserList and Browser classes for iOS.

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

Index: ios/clean/chrome/browser/model/browser.h
diff --git a/ios/clean/chrome/browser/model/browser.h b/ios/clean/chrome/browser/model/browser.h
new file mode 100644
index 0000000000000000000000000000000000000000..0e5349f84687719f8b6f40daf977806656e4b8e8
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+++ b/ios/clean/chrome/browser/model/browser.h
@@ -0,0 +1,34 @@
+// 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_H_
+#define IOS_CLEAN_CHROME_BROWSER_MODEL_BROWSER_H_
+
+#include "base/macros.h"
+#include "ios/shared/chrome/browser/tabs/web_state_list.h"
+
+namespace ios {
+class ChromeBrowserState;
+}
+
+// Browser holds the state backing a collection of Tabs and the attached
+// UI elements (Tab strip, ...).
+class Browser {
+ public:
+  explicit Browser(ios::ChromeBrowserState* browser_state);
+  ~Browser();
+
+  WebStateList& web_state_list() { return web_state_list_; }
+  const WebStateList& web_state_list() const { return web_state_list_; }
+
+  ios::ChromeBrowserState* browser_state() const { return browser_state_; }
+
+ private:
+  WebStateList web_state_list_;
+  ios::ChromeBrowserState* browser_state_;
+
+  DISALLOW_COPY_AND_ASSIGN(Browser);
+};
+
+#endif  // IOS_CLEAN_CHROME_BROWSER_MODEL_BROWSER_H_