media: add video capture device for ARC++ camera HAL v3

media/capture/video/linux/video_capture_device_factory_linux.cc

 // 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.
 
 #include "media/capture/video/linux/video_capture_device_factory_linux.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <stdint.h>
 #include <sys/ioctl.h>
@@ skipping 246 matching lines @@
   std::string usb_id;
   if (!ReadIdFile(vidPath, &usb_id))
     return "";
   usb_id.append(":");
   if (!ReadIdFile(pidPath, &usb_id))
     return "";
 
   return usb_id;
 }
 
+#if !defined(OS_CHROMEOS)

[wuchengli, 2017/04/28 06:29:28]

Try controlling this in media/capture/BUILD.gn. If we can't, explain why.

[jcliang, 2017/04/28 08:27:49]

There are rules in BUILDCONFIG.gn to control what files are compiled on each OS
platform:

https://cs.chromium.org/chromium/src/build/config/BUILDCONFIG.gn?q=BUILDCONFI...

ChromeOS is special in that is_chromeos and is_linux are both true, so all the
source files with _linux.* and _chromeos.* suffix are compile on chromeos. We
need to let the linux and chromeos coexist during the transition period, so I'm
using #define to control which factory gets created here.

We can fully control this in BUILD.gn once we fully remove dependency on the
V4L2 VCD on ChromeOS. 

 // static
 VideoCaptureDeviceFactory*
 VideoCaptureDeviceFactory::CreateVideoCaptureDeviceFactory(
     scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner) {
   return new VideoCaptureDeviceFactoryLinux(ui_task_runner);
 }
+#endif
 
 }  // namespace media