Add use_v4lplugin flag to enable v4l2 library

content/common/gpu/media/generic_v4l2_video_device.h

 // Copyright 2014 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.
 //
 // This file contains the implementation of GenericV4L2Device used on
 // platforms, which provide generic V4L2 video codec devices.
 
 #ifndef CONTENT_COMMON_GPU_MEDIA_GENERIC_V4L2_VIDEO_DEVICE_H_
 #define CONTENT_COMMON_GPU_MEDIA_GENERIC_V4L2_VIDEO_DEVICE_H_
 
@@ skipping 34 matching lines @@
   const Type type_;
 
   // The actual device fd.
   int device_fd_;
 
   // eventfd fd to signal device poll thread when its poll() should be
   // interrupted.
   int device_poll_interrupt_fd_;
 
   DISALLOW_COPY_AND_ASSIGN(GenericV4L2Device);
+
+  // Lazily initialize static data after sandbox is enabled.  Return false on
+  // init failure.
+  static bool PostSandboxInitialization();
 };
 }  //  namespace content
 
 #endif  // CONTENT_COMMON_GPU_MEDIA_GENERIC_V4L2_VIDEO_DEVICE_H_