Sort camera device list to use front camera first

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 210 matching lines @@
           VideoCaptureApi::LINUX_V4L2_SINGLE_PLANE,
           VideoCaptureTransportType::OTHER_TRANSPORT,
           g_camera_facing_helper.Get().GetCameraFacing(unique_id, model_id));
 #else
       device_descriptors->emplace_back(
           reinterpret_cast<char*>(cap.card), unique_id, model_id,
           VideoCaptureApi::LINUX_V4L2_SINGLE_PLANE);
 #endif
     }
   }
+#if defined(OS_CHROMEOS)
+  // Since JS doesn't have API to get camera facing, we sort the list to make
+  // apps can use the front camera by default.

[mcasas, 2017/01/25 17:35:15]

nit: s/to make apps can use/to make sure apps use/ ?

[henryhsu, 2017/01/26 02:22:54]

Done.

+  // TODO(henryhsu): remove this after JS API completed (crbug.com/543997).

[Guido Urdaneta, 2017/01/25 10:24:47]

Is this comment valid?
It is true that once crbug.com/543997 is fixed, constraints can be used to
specify which camera to use based on facing mode.
However, what about the case when no constraint is specified so that all cameras
are equally valid?
In this case the implementation needs a tie-breaking rule.
Would you prefer the tie breaker to choose front cameras over other cameras? If
so, the tie breaker could be implemented by preferring cameras that appear first
in the enumeration, so this ordering might need to be kept even after
crbug.com/543997.

[henryhsu, 2017/01/25 10:38:01]

Once crbug.com/543997 is fixed, caller should have all information to decide
which camera should be opened. The preference logic should be moved to caller
(camera app). So all cameras here are equal.

+  std::sort(device_descriptors->begin(), device_descriptors->end());
+#endif
 }
 
 void VideoCaptureDeviceFactoryLinux::GetSupportedFormats(
     const VideoCaptureDeviceDescriptor& device,
     VideoCaptureFormats* supported_formats) {
   DCHECK(thread_checker_.CalledOnValidThread());
   if (device.device_id.empty())
     return;
   base::ScopedFD fd(HANDLE_EINTR(open(device.device_id.c_str(), O_RDONLY)));
   if (!fd.is_valid())  // Failed to open this device.
@@ skipping 28 matching lines @@
 }
 
 // static
 VideoCaptureDeviceFactory*
 VideoCaptureDeviceFactory::CreateVideoCaptureDeviceFactory(
     scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner) {
   return new VideoCaptureDeviceFactoryLinux(ui_task_runner);
 }
 
 }  // namespace media