Fix NPE when onDestroy called

 Bug: 3177111
 Fixes a NPE when Service.onDestroy was called.

Change-Id: I30b75a4e4e71be8d04399b5e82e05f27eba5667c
diff --git a/src/com/android/browser/widget/BookmarkListWidgetService.java b/src/com/android/browser/widget/BookmarkListWidgetService.java
index 1b3b1f4..f0dd9cb 100644
--- a/src/com/android/browser/widget/BookmarkListWidgetService.java
+++ b/src/com/android/browser/widget/BookmarkListWidgetService.java
@@ -68,7 +68,6 @@
 
     private Map<Integer, BookmarkFactory> mFactories;
     private Handler mUiHandler;
-    private HandlerThread mBackgroundThread;
     private BookmarksObserver mBookmarksObserver;
 
     @Override
@@ -111,7 +110,6 @@
     public void onDestroy() {
         super.onDestroy();
         getContentResolver().unregisterContentObserver(mBookmarksObserver);
-        mBackgroundThread.quit();
     }
 
     private class BookmarksObserver extends ContentObserver {