Fix bug with invalid chrome.sessions.onChanged listener.

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

Index: chrome/browser/extensions/api/sessions/sessions_api.h
diff --git a/chrome/browser/extensions/api/sessions/sessions_api.h b/chrome/browser/extensions/api/sessions/sessions_api.h
index de6e9e7db3f56ea75c5c7f252c6ca13bc18bad34..832dd67ee3236d9bc8a0cd61ac11319a966a1a74 100644
--- a/chrome/browser/extensions/api/sessions/sessions_api.h
+++ b/chrome/browser/extensions/api/sessions/sessions_api.h
@@ -85,7 +85,8 @@ class SessionsRestoreFunction : public ChromeSyncExtensionFunction {
 
 class SessionsEventRouter : public sessions::TabRestoreServiceObserver {
  public:
-  explicit SessionsEventRouter(Profile* profile);
+  explicit SessionsEventRouter(Profile* profile,
+                               EventRouter::Observer* observer);
   ~SessionsEventRouter() override;
 
   // Observer callback for TabRestoreServiceObserver. Sends data on
@@ -100,6 +101,7 @@ class SessionsEventRouter : public sessions::TabRestoreServiceObserver {
 
  private:
   Profile* profile_;
+  EventRouter::Observer* observer_;
 
   // TabRestoreService that we are observing.
   sessions::TabRestoreService* tab_restore_service_;