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..006a27f27c9a584848b9b7ac855af916d79cc0a6 100644
--- a/media/capture/video/video_capture_device_descriptor.cc
+++ b/media/capture/video/video_capture_device_descriptor.cc
@@ -43,6 +43,19 @@ VideoCaptureDeviceDescriptor::~VideoCaptureDeviceDescriptor() {}
 VideoCaptureDeviceDescriptor::VideoCaptureDeviceDescriptor(
     const VideoCaptureDeviceDescriptor& other) = default;
 
+bool VideoCaptureDeviceDescriptor::operator<(
+    const VideoCaptureDeviceDescriptor& other) const {
+  int facing_mapping[NUM_MEDIA_VIDEO_FACING_MODE] = {0};

[Guido Urdaneta, 2017/01/25 10:27:23]

nit: I don't think you need the {0} initialization, but up to you.

+  facing_mapping[MEDIA_VIDEO_FACING_USER] = 2;
+  facing_mapping[MEDIA_VIDEO_FACING_ENVIRONMENT] = 1;
+  facing_mapping[MEDIA_VIDEO_FACING_NONE] = 0;

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

I'd do:

static const int kFacingMapping[] = {0, 1, 2};
static_assert(kFacingMapping(MEDIA_VIDEO_FACING_NONE == 0, "None");
static_assert(kFacingMapping(MEDIA_VIDEO_FACING_ENVIRONMENT == 1, "blabla");
static_assert(kFacingMapping(MEDIA_VIDEO_FACING_USER == 2, "bla");

so the correspondence would be enforced at compile time,
and the penalty of initializing the array is taken once.

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

Done.

+  if (facing_mapping[facing] > facing_mapping[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: