Add support for PTZ via VISCA.

extensions/common/api/webcam_private.idl

 // Copyright 2014 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.
 
 // Webcam Private API.
 namespace webcamPrivate {
   enum PanDirection { stop, right, left };
   enum TiltDirection { stop, up, down };
+  enum Protocol { visca };
+
+  dictionary ProtocolConfiguration {
+    Protocol? protocol;
+  };
 
   dictionary WebcamConfiguration {
     double? pan;
     PanDirection? panDirection;
     double? tilt;
     TiltDirection? tiltDirection;
     double? zoom;
   };
 
+  callback WebcamIdCallback = void(DOMString webcamId);
   callback WebcamConfigurationCallback =
       void(WebcamConfiguration configuration);
 
   interface Functions {
+    // Open a serial port that controls a webcam.
+    static void openSerialWebcam(DOMString path, ProtocolConfiguration protocol,
+                                 WebcamIdCallback callback);
+
+    // Close a serial port connection to a webcam.
+    static void closeWebcam(DOMString webcamId);
+
     static void get(DOMString webcamId, WebcamConfigurationCallback callback);
     static void set(DOMString webcamId, WebcamConfiguration config);
     static void reset(DOMString webcamId, WebcamConfiguration config);
   };
 };