Add visibility restrictions to all mojoms that export symbols.

device/generic_sensor/public/interfaces/BUILD.gn

 # Copyright 2016 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.
 
 import("//mojo/public/tools/bindings/mojom.gni")
 
 mojom("interfaces") {
+  visibility = [ "//device/generic_sensor/public/cpp" ]
+  visibility_blink = [ "//third_party/WebKit/Source/*" ]
   export_class_attribute = "DEVICE_GENERIC_SENSOR_PUBLIC_EXPORT"
   export_define = "DEVICE_GENERIC_SENSOR_PUBLIC_IMPLEMENTATION=1"
   export_header =
       "device/generic_sensor/public/cpp/generic_sensor_public_export.h"
   sources = [
     "sensor.mojom",
     "sensor_provider.mojom",
   ]
 }