Set drawable for the entity header app preference button.

In the entity header layout, the action buttons resource is set to null by
default. When we bind the button with the app preference action, we
should also set the drawable to the settings icon as well.

Change-Id: Ic259b4c538f529671ca5a9c67664ef32fbbb25ae
Fixes: 64826061
Test: make RunSettingsRoboTests

src/com/android/settings/widget/EntityHeaderController.java

@@ -336,6 +336,7 @@ public class EntityHeaderController {
                 final Intent intent = resolveIntent(
                         new Intent(Intent.ACTION_APPLICATION_PREFERENCES).setPackage(mPackageName));
                 if (intent == null) {
+                    button.setImageDrawable(null);
                     button.setVisibility(View.GONE);
                     return;
                 }
@@ -348,6 +349,7 @@ public class EntityHeaderController {
                         mFragment.startActivity(intent);
                     }
                 });
+                button.setImageResource(R.drawable.ic_settings_24dp);
                 button.setVisibility(View.VISIBLE);
                 return;
             }