Add support for PTZ via VISCA.

extensions/common/api/webcam_private.idl

Index: extensions/common/api/webcam_private.idl
diff --git a/extensions/common/api/webcam_private.idl b/extensions/common/api/webcam_private.idl
index 757e5b383c5518489256d3378cb79bf6ad471f4b..3fd629dc1141c64585ff2a39603cde916752bab4 100644
--- a/extensions/common/api/webcam_private.idl
+++ b/extensions/common/api/webcam_private.idl
@@ -6,6 +6,11 @@
 namespace webcamPrivate {
   enum PanDirection { stop, right, left };
   enum TiltDirection { stop, up, down };
+  enum Protocol { visca };
+
+  dictionary ProtocolConfiguration {
+    Protocol? protocol;
+  };
 
   dictionary WebcamConfiguration {
     double? pan;
@@ -15,10 +20,18 @@ namespace webcamPrivate {
     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);