Prevent apps from displaying over Settings

Specifically, the DrawOverlayDetails fragment only.

Bug: 36070413
Test: make RunSettingsRoboTests -j100
Change-Id: I0069f0cacf8c963c8c6878dc89a32b205983a568

src/com/android/settings/core/TouchOverlayManager.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2017 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
+ */
+
+package com.android.settings.core;
+
+import android.app.AppOpsManager;
+import android.content.Context;
+import android.os.Binder;
+import android.os.IBinder;
+
+public class TouchOverlayManager {
+
+    private final Context mContext;
+    private final IBinder mToken = new Binder();
+
+    public TouchOverlayManager(Context context) {
+        mContext = context;
+    }
+
+    public void setOverlayAllowed(boolean allowed) {
+        final AppOpsManager aom = mContext.getSystemService(AppOpsManager.class);
+        if (aom != null) {
+            aom.setUserRestriction(AppOpsManager.OP_SYSTEM_ALERT_WINDOW, !allowed, mToken);
+            aom.setUserRestriction(AppOpsManager.OP_TOAST_WINDOW, !allowed, mToken);
+        }
+    }
+}