Pass camera facing to WebKit

third_party/WebKit/public/platform/WebMediaStreamTrack.h

Index: third_party/WebKit/public/platform/WebMediaStreamTrack.h
diff --git a/third_party/WebKit/public/platform/WebMediaStreamTrack.h b/third_party/WebKit/public/platform/WebMediaStreamTrack.h
index d9191b721badcf0e80afb731e5014a181312a689..d531fbb760aa246efa2db2721f250de6eefc3882 100644
--- a/third_party/WebKit/public/platform/WebMediaStreamTrack.h
+++ b/third_party/WebKit/public/platform/WebMediaStreamTrack.h
@@ -42,6 +42,8 @@ class WebString;
 class WebMediaStreamTrack {
  public:
   struct Settings {
+    // TODO(hta): b/34118695. Consider to rename it to FacingMode.

[jochen (gone - plz use gerrit), 2017/01/11 13:23:27]

as a rule of thumb, please never refer to buganizer in chromium sources

[shenghao, 2017/01/12 08:10:49]

Done.

+    enum VideoFacingMode { User, Environment, Left, Right };
     bool hasFrameRate() { return frameRate >= 0.0; }
     bool hasWidth() { return width >= 0; }
     bool hasHeight() { return height >= 0; }
@@ -51,6 +53,7 @@ class WebMediaStreamTrack {
     long width = -1;
     long height = -1;
     WebString deviceId;
+    VideoFacingMode facingMode = VideoFacingMode::User;

[mcasas, 2017/01/11 22:24:59]

I made a comment that's possibly lost in the review:
I don't like that, as-is, AudioTracks, or even VideoTracks 
coming from a Screen/Tab/Desktop/<canvas>/<video>
can also have a "facingMode" :-S

I propose making this field [1] a base::Optional<VideoFacingMode>
so that, if it's not applicable, we can return an empty string to 
the JS user.  base::Optional is perfect for this case [2]:

"A very common use case is for classes and structures 
 that have an object not always available, because it is 
 early initialized or because the underlying data 
 structure doesn't require it."

[1]
https://cs.chromium.org/chromium/src/base/optional.h?q=base::optional&sq=pack...
[2]
https://chromium.googlesource.com/chromium/src/+/master/docs/optional.md#When...

[shenghao, 2017/01/12 08:10:49]

Done.

   };
 
   class TrackData {