[sensors] Add Permission guard to the generic sensor apis.

chrome/test/data/generic_sensor/sensor.js

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+var timeOrigin;
+var sensor;
+
+function notifyTestDone() {
+  window.domAutomationController.send(true);
+}
+
+function onAmbientLightReadingChange() {
+  if (sensor.illuminance == 50 &&
+      sensor.timestamp > timeOrigin &&
+      sensor.timestamp < window.performance.now()) {
+    pass();
+  } else {
+    fail();
+  }
+  notifyTestDone();
+}
+
+function onSensorFailed() {
+  notifyTestDone();
+}
+
+function triggerSensorStart() {
+  sensor = new AmbientLightSensor();
+  timeOrigin = window.performance.now();
+  sensor.onchange =
+      onAmbientLightReadingChange;
+  sensor.onerror = onSensorFailed;
+  sensor.start();
+}
+
+function pass() {
+  document.getElementById('status').innerHTML = 'PASS';
+  document.location = '#pass';
+}
+
+function fail() {
+  document.location = '#fail';
+}
+