Sort camera device list to use front camera first

media/capture/video/video_capture_device_descriptor.cc

Index: media/capture/video/video_capture_device_descriptor.cc
diff --git a/media/capture/video/video_capture_device_descriptor.cc b/media/capture/video/video_capture_device_descriptor.cc
index f1e288cbe32954ee07a9a6de78c723e2a37b3bb2..51aa3f02e7e1bb83a0f41863cf10f3e10d81a530 100644
--- a/media/capture/video/video_capture_device_descriptor.cc
+++ b/media/capture/video/video_capture_device_descriptor.cc
@@ -4,6 +4,8 @@
 
 #include "media/capture/video/video_capture_device_descriptor.h"
 
+#include <map>
+
 #include "base/logging.h"
 
 namespace media {
@@ -43,6 +45,19 @@ VideoCaptureDeviceDescriptor::~VideoCaptureDeviceDescriptor() {}
 VideoCaptureDeviceDescriptor::VideoCaptureDeviceDescriptor(
     const VideoCaptureDeviceDescriptor& other) = default;
 
+bool VideoCaptureDeviceDescriptor::operator<(
+    const VideoCaptureDeviceDescriptor& other) const {
+  std::map<media::VideoFacingMode, size_t> facing_mapping{

[Guido Urdaneta, 2017/01/24 10:42:07]

nit: Optional. the map is fine, but maybe you can also use an array:
int facing_mapping[NUM_MEDIA_VIDEO_FACING_MODE];
facing_mapping[MEDIA_VIDEO_FACING_USER] = 0;
facing_mapping[MEDIA_VIDEO_FACING_ENVIRONMENT] = 1;
facing_mapping[MEDIA_VIDEO_FACING_NONE] = 2;

[henryhsu, 2017/01/25 03:28:18]

Done.

+      {MEDIA_VIDEO_FACING_USER, 0},
+      {MEDIA_VIDEO_FACING_ENVIRONMENT, 1},
+      {MEDIA_VIDEO_FACING_NONE, 2}};
+  if (facing_mapping.at(facing) < facing_mapping.at(other.facing))
+    return true;
+  if (device_id < other.device_id)
+    return true;
+  return capture_api < other.capture_api;
+}
+
 const char* VideoCaptureDeviceDescriptor::GetCaptureApiTypeString() const {
   switch (capture_api) {
     case VideoCaptureApi::LINUX_V4L2_SINGLE_PLANE: