Now closes existing background contents if app opens a new one.

chrome/browser/background/background_contents_service.cc

Index: chrome/browser/background/background_contents_service.cc
diff --git a/chrome/browser/background/background_contents_service.cc b/chrome/browser/background/background_contents_service.cc
index bc3e6062d18e3acdb8dd3919983c16d67f048ab2..9191ddb4ecab14bc33616d7e7e54d9f49812e8b5 100644
--- a/chrome/browser/background/background_contents_service.cc
+++ b/chrome/browser/background/background_contents_service.cc
@@ -354,10 +354,13 @@ void BackgroundContentsService::LoadBackgroundContentsFromPrefs(
       // We should never reach here - it should not be possible for an app
       // to become uninstalled without the associated BackgroundContents being
       // unregistered via the EXTENSIONS_UNLOADED notification, unless there's a
-      // crash before we could save our prefs.
+      // crash before we could save our prefs, or if the user deletes the
+      // extension files manually rather than uninstalling it.
       NOTREACHED() << "No extension found for BackgroundContents - id = "
                    << *it;
-      return;
+      // Don't cancel out of our loop, just ignore this BackgroundContents and
+      // load the next one.
+      continue;
     }
     LoadBackgroundContentsFromDictionary(profile, *it, contents);
   }