Make BrowserList::(Add|Remove)Observer add the observer to every desktop's browser list.

chrome/browser/ui/browser_list.h

 // Copyright (c) 2012 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_UI_BROWSER_LIST_H_
 #define CHROME_BROWSER_UI_BROWSER_LIST_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
 
 class Browser;
 class Profile;
 
 namespace chrome {
 class BrowserListObserver;
 }
 
 // Stores a list of all Browser objects.
 class BrowserList {
  public:
   typedef std::vector<Browser*> BrowserVector;
   typedef BrowserVector::const_reverse_iterator const_reverse_iterator;
 
-  // Adds and removes browsers from the global list. The browser object should
-  // be valid BEFORE these calls (for the benefit of observers), so notify and
-  // THEN delete the object.
+  // Adds and removes browsers from the list they are associated with. The
+  // browser object should be valid BEFORE these calls (for the benefit of
+  // observers), so notify and THEN delete the object.
   static void AddBrowser(Browser* browser);
   static void RemoveBrowser(Browser* browser);
 
+  // Adds and removes |observer| from the observer list of each desktop.
   static void AddObserver(chrome::BrowserListObserver* observer);
   static void RemoveObserver(chrome::BrowserListObserver* observer);
 
   // Called by Browser objects when their window is activated (focused).  This
   // allows us to determine what the last active Browser was.
   static void SetLastActive(Browser* browser);
 
   // Closes all browsers for |profile| across all desktops.
   static void CloseAllBrowsersWithProfile(Profile* profile);
 
   // Returns iterated access to list of open browsers ordered by when
   // they were last active. The underlying data structure is a vector
   // and we push_back on recent access so a reverse iterator gives the
   // latest accessed browser first.
   static const_reverse_iterator begin_last_active();
   static const_reverse_iterator end_last_active();
 
   // Returns true if at least one incognito session is active.
   static bool IsOffTheRecordSessionActive();
 
   // Returns true if at least one incognito session is active for |profile|.
   static bool IsOffTheRecordSessionActiveForProfile(Profile* profile);
 };
 
 #endif  // CHROME_BROWSER_UI_BROWSER_LIST_H_