Sort camera device list to use front camera first

media/capture/video/video_capture_device_descriptor.h

 // 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.
 
 #ifndef MEDIA_CAPTURE_VIDEO_VIDEO_CAPTURE_DEVICE_DESCRIPTOR_H_
 #define MEDIA_CAPTURE_VIDEO_VIDEO_CAPTURE_DEVICE_DESCRIPTOR_H_
 
+#include <map>
 #include <string>
 #include <vector>
 
 #include "media/base/video_facing.h"
 #include "media/capture/capture_export.h"
 
 namespace media {
 
 // A Java counterpart will be generated for this enum.
 // GENERATED_JAVA_ENUM_PACKAGE: org.chromium.media
@@ skipping 42 matching lines @@
   VideoCaptureDeviceDescriptor(const VideoCaptureDeviceDescriptor& other);
   ~VideoCaptureDeviceDescriptor();
 
   // These operators are needed due to storing the name in an STL container.
   // In the shared build, all methods from the STL container will be exported
   // so even though they're not used, they're still depended upon.
   bool operator==(const VideoCaptureDeviceDescriptor& other) const {
     return (other.device_id == device_id) && (other.capture_api == capture_api);
   }
   bool operator<(const VideoCaptureDeviceDescriptor& other) const {
+    std::vector<media::VideoFacingMode> facing_prefer_list{
+        MEDIA_VIDEO_FACING_USER, MEDIA_VIDEO_FACING_ENVIRONMENT,
+        MEDIA_VIDEO_FACING_NONE,
+    };
+    std::map<media::VideoFacingMode, size_t> facing_mapping;
+    for (size_t i = 0; i < facing_prefer_list.size(); i++) {
+      facing_mapping[facing_prefer_list[i]] = i;
+    }

[hta - Chromium, 2017/01/24 09:46:24]

The two-step process here seems strange. Why not initialize the map?

... facing_mapping({{MEDIA_VIDEO_FACING_USER, 1},
 {MEDIA_VIDEO_FACING_ENVIRONMENT, 2},
 {MEDIA_VIDEO_FACING_NONE, 3}})

[henryhsu, 2017/01/24 10:26:40]

Done.

+    if (facing_mapping.at(facing) < facing_mapping.at(other.facing))

[hta - Chromium, 2017/01/24 09:46:24]

What happens here if facing = MEDIA_VIDEO_FACING_LEFT?

This enumeration at JS level has two more values - left and right. Sooner or
later these will percolate down to this level too.

[henryhsu, 2017/01/24 10:26:40]

It's impossible to have MEDIA_VIDEO_FACING_LEFT value. Because facing is
assigned by camera_facing_chromeos.cc not from JS level.
Please reference
https://codereview.chromium.org/2609863004/patch/400001/410012

+      return true;

[hta - Chromium, 2017/01/24 09:46:24]

I would expect a function this long to get hollered at by presubmit for being
"too long for a .cc"

We already have video_capture_device_descriptor.cc; suggest to move it there.

[henryhsu, 2017/01/24 10:26:40]

Done.

     if (device_id < other.device_id)
       return true;
     return capture_api < other.capture_api;
   }
 
   const char* GetCaptureApiTypeString() const;
   // Friendly name of a device, plus the model identifier in parentheses.
   std::string GetNameAndModel() const;
 
   std::string display_name;  // Name that is intended for display in the UI
   std::string device_id;
   // A unique hardware identifier of the capture device.
   // It is of the form "[vid]:[pid]" when a USB device is detected, and empty
   // otherwise.
   std::string model_id;
 
   VideoFacingMode facing;
 
   VideoCaptureApi capture_api;
   VideoCaptureTransportType transport_type;
 };
 
 using VideoCaptureDeviceDescriptors = std::vector<VideoCaptureDeviceDescriptor>;
 
 }  // namespace media
 
 #endif  // MEDIA_CAPTURE_VIDEO_VIDEO_CAPTURE_DEVICE_DESCRIPTOR_H_