Move handling of package changes to a background thread.

Helps get rid of some jank when installing applications.

Change-Id: I97d0022f82d67796e334d37086e5911dd6ca6b62
diff --git a/core/java/android/widget/ActivityChooserModel.java b/core/java/android/widget/ActivityChooserModel.java
index bc44521..c53b5f6 100644
--- a/core/java/android/widget/ActivityChooserModel.java
+++ b/core/java/android/widget/ActivityChooserModel.java
@@ -365,7 +365,7 @@
         } else {
             mHistoryFileName = historyFileName;
         }
-        mPackageMonitor.register(mContext, true);
+        mPackageMonitor.register(mContext, null, true);
     }
 
     /**