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

chrome/browser/ui/browser_list_impl.h

Index: chrome/browser/ui/browser_list_impl.h
diff --git a/chrome/browser/ui/browser_list_impl.h b/chrome/browser/ui/browser_list_impl.h
index 2801a6e2b0db02f192eac0ceb77d89d4dd848c14..3ff167ce54e92ee02af0fed8c85a123eb64d3c81 100644
--- a/chrome/browser/ui/browser_list_impl.h
+++ b/chrome/browser/ui/browser_list_impl.h
@@ -6,10 +6,10 @@
 #define CHROME_BROWSER_UI_BROWSER_LIST_IMPL_H_
 
 #include "base/observer_list.h"
+#include "chrome/browser/ui/browser_list.h"
 #include "chrome/browser/ui/host_desktop.h"
 
 class Browser;
-class BrowserList;
 class Profile;
 
 namespace chrome {
@@ -33,9 +33,6 @@ class BrowserListImpl {
   void AddBrowser(Browser* browser);
   void RemoveBrowser(Browser* browser);
 
-  void AddObserver(BrowserListObserver* observer);
-  void RemoveObserver(BrowserListObserver* observer);
-
   // Called by Browser objects when their window is activated (focused).  This
   // allows us to determine what the last active Browser was.
   void SetLastActive(Browser* browser);
@@ -73,6 +70,14 @@ class BrowserListImpl {
   BrowserListImpl();
   ~BrowserListImpl();
 
+  // Only callable by BrowserList::(Add|Remove)Observer.
+  // TODO(gab): Merge BrowserListImpl into BrowserList removing the need for
+  // friend.
+  friend void BrowserList::AddObserver(chrome::BrowserListObserver*);
+  friend void BrowserList::RemoveObserver(chrome::BrowserListObserver*);
+  void AddObserver(BrowserListObserver* observer);
+  void RemoveObserver(BrowserListObserver* observer);
+
   // Helper method to remove a browser instance from a list of browsers
   void RemoveBrowserFrom(Browser* browser, BrowserVector* browser_list);