Move implementation of BrowserList onto an inner, instantiatable class, BrowserListImpl.

chrome/browser/ui/browser_list_observer.h

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.

[tfarina, 2012/07/13 00:55:22]

Thanks for doing this! Although I had a patch in my branch here to extract
BrowserListObserver from BrowserList, but never had time to send to you :-(

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_UI_BROWSER_LIST_OBSERVER_H_
+#define CHROME_BROWSER_UI_BROWSER_LIST_OBSERVER_H_
+
+class Browser;
+
+namespace chrome {
+
+// Implementations must not change the contents of the BrowserList inside any
+// of these methods.
+class BrowserListObserver {
+  public:

[tfarina, 2012/07/13 00:55:22]

nit: indent one less space ;)

+  // Called immediately after a browser is added to the list
+  virtual void OnBrowserAdded(Browser* browser) {}
+
+  // Called immediately after a browser is removed from the list
+  virtual void OnBrowserRemoved(Browser* browser) {}
+
+  // Called immediately after a browser is set active (SetLastActive)
+  virtual void OnBrowserSetLastActive(Browser* browser) {}
+
+ protected:
+  virtual ~BrowserListObserver() {}
+};
+
+}  // namespace chrome
+
+#endif  // CHROME_BROWSER_UI_BROWSER_LIST_OBSERVER_H_