app_list::StartPageService: Document and check nulls.

chrome/browser/ui/app_list/start_page_service.h

 // Copyright 2013 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_APP_LIST_START_PAGE_SERVICE_H_
 #define CHROME_BROWSER_UI_APP_LIST_START_PAGE_SERVICE_H_
 
 #include <stdint.h>
 #include <string>
 #include <vector>
@@ skipping 37 matching lines @@
 
 // StartPageService collects data to be displayed in app list's start page
 // and hosts the start page contents.
 class StartPageService : public KeyedService,
                          public content::WebContentsObserver,
                          public net::URLFetcherDelegate,
                          public SpeechRecognizerDelegate {
  public:
   typedef std::vector<scoped_refptr<const extensions::Extension> >
       ExtensionList;
-  // Gets the instance for the given profile.
+  // Gets the instance for the given profile. May return nullptr.
   static StartPageService* Get(Profile* profile);
 
   void AddObserver(StartPageObserver* observer);
   void RemoveObserver(StartPageObserver* observer);
 
   void Init();
 
   // Loads the start page WebContents if it hasn't already been loaded.
   void LoadContentsIfNeeded();
 
@@ skipping 110 matching lines @@
   scoped_ptr<net::URLFetcher> doodle_fetcher_;
 
   base::WeakPtrFactory<StartPageService> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(StartPageService);
 };
 
 }  // namespace app_list
 
 #endif  // CHROME_BROWSER_UI_APP_LIST_START_PAGE_SERVICE_H_