Fix double divider in Apps & notifications page

- The second divider is shown after we set a background to the pinned
  header.
- Fix it by simply hiding the pinned header instead of its inner views.

Fixes: 133231218
Test: robotest, visual
Change-Id: I53add6f01930299425ce96d23350f9f066e85145

src/com/android/settings/SettingsPreferenceFragment.java

@@ -113,7 +113,8 @@ public abstract class SettingsPreferenceFragment extends InstrumentedPreferenceF
                 }
             };
 
-    private ViewGroup mPinnedHeaderFrameLayout;
+    @VisibleForTesting
+    ViewGroup mPinnedHeaderFrameLayout;
     private ViewGroup mButtonBar;
 
     private LayoutPreference mHeader;
@@ -186,6 +187,10 @@ public abstract class SettingsPreferenceFragment extends InstrumentedPreferenceF
         mPinnedHeaderFrameLayout.setVisibility(View.VISIBLE);
     }
 
+    public void showPinnedHeader(boolean show) {
+        mPinnedHeaderFrameLayout.setVisibility(show ? View.VISIBLE : View.INVISIBLE);
+    }
+
     @Override
     public void onSaveInstanceState(Bundle outState) {
         super.onSaveInstanceState(outState);