Do not allow add view in DeferredAppWidgetHostView

Also set rounded corners to DeferredAppWidgetHostView

Test: manual
Fix: 193885118
Change-Id: I663b5b4a50da1f2348be1792923ee73fe8e6a2e8

res/drawable-v31/bg_deferred_app_widget.xml

@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  Copyright (C) 2021 The Android Open Source Project
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+-->
+<inset xmlns:android="http://schemas.android.com/apk/res/android"
+    android:inset="8dp">
+    <shape android:shape="rectangle">
+        <corners android:radius="@android:dimen/system_app_widget_background_radius" />
+        <solid android:color="#77000000" />
+    </shape>
+</inset>

src/com/android/launcher3/widget/DeferredAppWidgetHostView.java

@@ -25,6 +25,7 @@ import android.text.StaticLayout;
 import android.text.TextPaint;
 import android.text.TextUtils;
 import android.util.TypedValue;
+import android.view.View;
 import android.widget.RemoteViews;
 
 import com.android.launcher3.R;
@@ -54,6 +55,11 @@ public class DeferredAppWidgetHostView extends LauncherAppWidgetHostView {
         // Not allowed
     }
 
+    @Override
+    public void addView(View child) {
+        // Not allowed
+    }
+
     @Override
     protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
         super.onMeasure(widthMeasureSpec, heightMeasureSpec);