Fix comment in MediaStreamManager::FinalizeGenerateStream

Change-Id: I8c30b541360493298675bad413c3e999220f3a77
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2209212
Auto-Submit: François Beaufort <beaufort.francois@gmail.com>
Commit-Queue: Guido Urdaneta <guidou@chromium.org>
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Cr-Commit-Position: refs/heads/master@{#770961}

content/browser/renderer_host/media/media_stream_manager.cc

@@ -1766,7 +1766,7 @@ void MediaStreamManager::FinalizeGenerateStream(const std::string& label,
   }
 
   // It is safe to bind base::Unretained(this) because MediaStreamManager is
-  // owned by BrowserMainLoop and so guaranteed to be approximately immortal.
+  // owned by BrowserMainLoop and so outlives the IO thread.
   base::PostTaskAndReplyWithResult(
       FROM_HERE, {BrowserThread::UI},
       base::BindOnce(&MediaDevicesPermissionChecker::