Sort camera device list to use front camera first

media/capture/video/video_capture_device_descriptor.cc

 // Copyright 2016 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/video_capture_device_descriptor.h"
 
 #include "base/logging.h"
 
 namespace media {
 
@@ skipping 25 matching lines @@
       model_id(model_id),
       facing(facing),
       capture_api(capture_api),
       transport_type(transport_type) {}
 
 VideoCaptureDeviceDescriptor::~VideoCaptureDeviceDescriptor() {}
 
 VideoCaptureDeviceDescriptor::VideoCaptureDeviceDescriptor(
     const VideoCaptureDeviceDescriptor& other) = default;
 
+bool VideoCaptureDeviceDescriptor::operator<(
+    const VideoCaptureDeviceDescriptor& other) const {
+  static constexpr int kFacingMapping[NUM_MEDIA_VIDEO_FACING_MODE] = {0, 2, 1};
+  static_assert(kFacingMapping[MEDIA_VIDEO_FACING_NONE] == 0,
+                "FACING_NONE has a wrong value");
+  static_assert(kFacingMapping[MEDIA_VIDEO_FACING_ENVIRONMENT] == 1,
+                "FACING_ENVIRONMENT has a wrong value");
+  static_assert(kFacingMapping[MEDIA_VIDEO_FACING_USER] == 2,
+                "FACING_USER has a wrong value");
+  if (kFacingMapping[facing] > kFacingMapping[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:
       return "V4L2 SPLANE";
     case VideoCaptureApi::WIN_MEDIA_FOUNDATION:
       return "Media Foundation";
     case VideoCaptureApi::WIN_DIRECT_SHOW:
       return "Direct Show";
     case VideoCaptureApi::MACOSX_AVFOUNDATION:
       return "AV Foundation";
@@ skipping 16 matching lines @@
   }
 }
 
 std::string VideoCaptureDeviceDescriptor::GetNameAndModel() const {
   if (model_id.empty())
     return display_name;
   return display_name + " (" + model_id + ")";
 }
 
 }  // namespace media