Sort camera device list to use front camera first

media/capture/video/video_capture_device_descriptor.h

Index: media/capture/video/video_capture_device_descriptor.h
diff --git a/media/capture/video/video_capture_device_descriptor.h b/media/capture/video/video_capture_device_descriptor.h
index 84ff841dbf4347b67cc29e1534f66bd6cf7c1c53..5ec1c4ca8234a78528b66e17e0bddba1155ade11 100644
--- a/media/capture/video/video_capture_device_descriptor.h
+++ b/media/capture/video/video_capture_device_descriptor.h
@@ -5,6 +5,7 @@
 #ifndef MEDIA_CAPTURE_VIDEO_VIDEO_CAPTURE_DEVICE_DESCRIPTOR_H_
 #define MEDIA_CAPTURE_VIDEO_VIDEO_CAPTURE_DEVICE_DESCRIPTOR_H_
 
+#include <map>
 #include <string>
 #include <vector>
 
@@ -67,6 +68,16 @@ struct CAPTURE_EXPORT VideoCaptureDeviceDescriptor {
     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;