Use a valid ChromeOS #define in MediaNotificationServiceFactory

MediaNotificationServiceFactory uses a non-existent #define for
ChromeOS, defined(CHROME_OS), we should replace it with
defined(OS_CHROMEOS).

Bug: 1121653
Change-Id: Idd748e7e49c9b2bdc675ae55f1c2b49a6c5ee28b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2436169Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Lan Wei <lanwei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811522}

chrome/browser/ui/global_media_controls/media_notification_service_factory.cc

@@ -35,7 +35,7 @@ MediaNotificationService* MediaNotificationServiceFactory::GetForProfile(
 KeyedService* MediaNotificationServiceFactory::BuildServiceInstanceFor(
     content::BrowserContext* context) const {
   bool show_from_all_profiles = false;
-#if defined(CHROME_OS)
+#if defined(OS_CHROMEOS)
   show_from_all_profiles = true;
 #endif
   return new MediaNotificationService(Profile::FromBrowserContext(context),