Implement sidebar support for extension action popups

chrome/browser/extensions/sidebar_manager_observer.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 CHROME_BROWSER_EXTENSIONS_SIDEBAR_MANAGER_OBSERVER_H_
+#define CHROME_BROWSER_EXTENSIONS_SIDEBAR_MANAGER_OBSERVER_H_
+
+namespace content {
+class WebContents;
+};
+
+class SidebarManagerObserver {
+ public:
+  virtual ~SidebarManagerObserver() {}
+
+  // Called when sidebar is shown.
+  virtual void OnSidebarShown(content::WebContents* tab,
+                              const std::string& content_id) {}
+
+  // Called when sidebar is hidden.
+  virtual void OnSidebarHidden(content::WebContents* tab,
+                               const std::string& content_id) {}
+
+};
+
+#endif  // CHROME_BROWSER_EXTENSIONS_SIDEBAR_MANAGER_OBSERVER_H_