Begin adding support for tab mirroring via the MediaStream audio/video capturing

content/public/common/media_stream_request.h

Index: content/public/common/media_stream_request.h
diff --git a/content/public/common/media_stream_request.h b/content/public/common/media_stream_request.h
index b383a31bb2c659f202b94d70c3da68676fa503cd..338844a21570f912c2f0eb96731baeb8a2e6b907 100644
--- a/content/public/common/media_stream_request.h
+++ b/content/public/common/media_stream_request.h
@@ -18,11 +18,23 @@ namespace content {
 // Types of media streams.
 enum MediaStreamDeviceType {
   MEDIA_STREAM_DEVICE_TYPE_NO_SERVICE = 0,
-  MEDIA_STREAM_DEVICE_TYPE_AUDIO_CAPTURE,
-  MEDIA_STREAM_DEVICE_TYPE_VIDEO_CAPTURE,
+
+  // A user device provided by the operating system (e.g., webcam input).
+  MEDIA_STREAM_DEVICE_TYPE_USER_AUDIO_CAPTURE,
+  MEDIA_STREAM_DEVICE_TYPE_USER_VIDEO_CAPTURE,
+
+  // Mirroring of a browser tab.
+  MEDIA_STREAM_DEVICE_TYPE_TAB_AUDIO_CAPTURE,
+  MEDIA_STREAM_DEVICE_TYPE_TAB_VIDEO_CAPTURE,
+
   NUM_MEDIA_STREAM_DEVICE_TYPES
 };
 
+// Convenience predicates to determine whether the given type represents some
+// audio or some video device.
+CONTENT_EXPORT bool IsAudioMediaStreamDeviceType(MediaStreamDeviceType type);
+CONTENT_EXPORT bool IsVideoMediaStreamDeviceType(MediaStreamDeviceType type);
+
 // TODO(xians): Change the structs to classes.
 // Represents one device in a request for media stream(s).
 struct CONTENT_EXPORT MediaStreamDevice {