Fix the build.

Change-Id: I9b9e26e22a6be27341f4b0b95cb8edd1629fa812
diff --git a/core/java/android/widget/ActivityChooserModel.java b/core/java/android/widget/ActivityChooserModel.java
index 1578154..c6104bc 100644
--- a/core/java/android/widget/ActivityChooserModel.java
+++ b/core/java/android/widget/ActivityChooserModel.java
@@ -21,6 +21,7 @@
 import android.content.Intent;
 import android.content.pm.ResolveInfo;
 import android.database.DataSetObservable;
+import android.database.DataSetObserver;
 import android.os.AsyncTask;
 import android.text.TextUtils;
 import android.util.Log;