Fix bug with invalid chrome.sessions.onChanged listener.

chrome/browser/extensions/api/sessions/sessions_api.cc

Index: chrome/browser/extensions/api/sessions/sessions_api.cc
diff --git a/chrome/browser/extensions/api/sessions/sessions_api.cc b/chrome/browser/extensions/api/sessions/sessions_api.cc
index 6d6810a2f8f3c688839d2b3dc215c23b18b25f12..6fe3b8b4f231bd996d8abe5f6526e53b126d2afb 100644
--- a/chrome/browser/extensions/api/sessions/sessions_api.cc
+++ b/chrome/browser/extensions/api/sessions/sessions_api.cc
@@ -607,8 +607,10 @@ bool SessionsRestoreFunction::RunSync() {
       : RestoreLocalSession(*session_id, browser);
 }
 
-SessionsEventRouter::SessionsEventRouter(Profile* profile)
+SessionsEventRouter::SessionsEventRouter(Profile* profile,
+                                         EventRouter::Observer* observer)
     : profile_(profile),
+      observer_(observer),
       tab_restore_service_(TabRestoreServiceFactory::GetForProfile(profile)) {
   // TabRestoreServiceFactory::GetForProfile() can return NULL (i.e., when in
   // incognito mode)
@@ -634,6 +636,8 @@ void SessionsEventRouter::TabRestoreServiceChanged(
 void SessionsEventRouter::TabRestoreServiceDestroyed(
     sessions::TabRestoreService* service) {
   tab_restore_service_ = NULL;
+  EventRouter::Get(profile_)->RegisterObserver(
+      observer_, api::sessions::OnChanged::kEventName);
 }
 
 SessionsAPI::SessionsAPI(content::BrowserContext* context)
@@ -659,7 +663,8 @@ SessionsAPI::GetFactoryInstance() {
 
 void SessionsAPI::OnListenerAdded(const EventListenerInfo& details) {
   sessions_event_router_.reset(
-      new SessionsEventRouter(Profile::FromBrowserContext(browser_context_)));
+      new SessionsEventRouter(Profile::FromBrowserContext(browser_context_),
+                              this));
   EventRouter::Get(browser_context_)->UnregisterObserver(this);
 }