Improve Preference highlighting

- add PreferenceFragment.onBindPreferences() so that we can know
when the binding as been done
- use the Preference's key as a tag for its View (so that we can
locate it latter in the View hierarchy)

Change-Id: Ifb3b30e576048b7464af63643834d278a46a8543

core/java/android/preference/PreferenceFragment.java

@@ -329,6 +329,11 @@ public abstract class PreferenceFragment extends Fragment implements
         if (preferenceScreen != null) {
             preferenceScreen.bind(getListView());
         }
+        onBindPreferences();
+    }
+
+    /** @hide */
+    protected void onBindPreferences() {
     }
 
     /** @hide */

core/java/android/preference/PreferenceGroupAdapter.java

@@ -20,7 +20,6 @@ import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 
-import android.graphics.Rect;
 import android.graphics.drawable.Drawable;
 import android.os.Handler;
 import android.preference.Preference.OnPreferenceChangeInternalListener;
@@ -243,6 +242,7 @@ public class PreferenceGroupAdapter extends BaseAdapter
         if (position == mHighlightedPosition && mHighlightedDrawable != null) {
             result.setBackgroundDrawable(mHighlightedDrawable);
         }
+        result.setTag(preference.getKey());
         return result;
     }