Add Observer in FaviconTabHelper

chrome/browser/favicon/favicon_tab_helper_observer.h

+// Copyright 2014 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_FAVICON_FAVICON_TAB_HELPER_OBSERVER_H_
+#define CHROME_BROWSER_FAVICON_FAVICON_TAB_HELPER_OBSERVER_H_
+
+namespace gfx {
+class Image;
+}
+
+// An observer implemented by classes which are interested in envent in
+// FaviconTabHelper.
+class FaviconTabHelperObserver {
+ public:
+  // Called when favicon |image| is retrieved from either web site or history
+  // backend.
+  virtual void OnFaviconAvailable(const gfx::Image& image) = 0;
+
+ protected:
+  virtual ~FaviconTabHelperObserver() {}
+};
+
+#endif  // CHROME_BROWSER_FAVICON_FAVICON_TAB_HELPER_OBSERVER_H_