ImageCapture: Implement TakePhoto() for Linux/CrOs

media/capture/video/linux/video_capture_device_linux.cc

Index: media/capture/video/linux/video_capture_device_linux.cc
diff --git a/media/capture/video/linux/video_capture_device_linux.cc b/media/capture/video/linux/video_capture_device_linux.cc
index c6ddd2b070a4d5434102091bb84743dba60046a1..a9f2aebad2c0102c8aba52d339032292100cb301 100644
--- a/media/capture/video/linux/video_capture_device_linux.cc
+++ b/media/capture/video/linux/video_capture_device_linux.cc
@@ -82,6 +82,16 @@ void VideoCaptureDeviceLinux::StopAndDeAllocate() {
   capture_impl_ = NULL;

[mcasas, 2016/09/16 03:50:37]

nit: not your code, but can you s/NULL/nullptr/ plz?

[xianglu, 2016/09/16 18:22:34]

Done.

 }
 
+void VideoCaptureDeviceLinux::TakePhoto(TakePhotoCallback callback) {
+  DCHECK(capture_impl_);
+  DCHECK(v4l2_thread_.IsRunning());

[mcasas, 2016/09/16 03:50:37]

This should be a 
if (!v4l2_thread_.IsRunning())
  return;

otherwise when DCHECK()s are disconnected
(i.e. in a Release build), we'd crash in l.90.

[xianglu, 2016/09/16 18:22:34]

Done.

+  DVLOG(1) << "in VCDLinux: TakePhoto() is called";

[mcasas, 2016/09/16 03:50:37]

nit: Remove this. In any case, it should be
before the DCHECK()s (so if they are hit, you'd
still see something), and using __func__:

DVLOG(1) << __func__;

[xianglu, 2016/09/16 18:22:34]

Done.

+
+  v4l2_thread_.task_runner()->PostTask(
+      FROM_HERE, base::Bind(&V4L2CaptureDelegate::TakePhoto, capture_impl_,
+                            base::Passed(&callback)));
+}
+
 void VideoCaptureDeviceLinux::SetRotation(int rotation) {
   if (v4l2_thread_.IsRunning()) {
     v4l2_thread_.task_runner()->PostTask(