[ios] Add a delegate to WebStateList class.

ios/shared/chrome/browser/tabs/fake_web_state_list_delegate.h

Index: ios/shared/chrome/browser/tabs/fake_web_state_list_delegate.h
diff --git a/ios/shared/chrome/browser/tabs/fake_web_state_list_delegate.h b/ios/shared/chrome/browser/tabs/fake_web_state_list_delegate.h
new file mode 100644
index 0000000000000000000000000000000000000000..ff499e9e4a9fc5a2e13df6191fe0f460faf74076
--- /dev/null
+++ b/ios/shared/chrome/browser/tabs/fake_web_state_list_delegate.h
@@ -0,0 +1,24 @@
+// 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_SHARED_CHROME_BROWSER_TABS_FAKE_WEB_STATE_LIST_DELEGATE_H_
+#define IOS_SHARED_CHROME_BROWSER_TABS_FAKE_WEB_STATE_LIST_DELEGATE_H_
+
+#include "base/macros.h"
+#import "ios/shared/chrome/browser/tabs/web_state_list_delegate.h"
+
+// Fake WebStateList delegate for tests.
+class FakeWebStateListDelegate : public WebStateListDelegate {
+ public:
+  FakeWebStateListDelegate();
+  ~FakeWebStateListDelegate() override;
+
+  // WebStateListDelegate implementation.
+  void WillAddWebState(web::WebState* web_state) override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(FakeWebStateListDelegate);
+};
+
+#endif  // IOS_SHARED_CHROME_BROWSER_TABS_FAKE_WEB_STATE_LIST_DELEGATE_H_