feat(castable-video): Add castCustomData to send arbitrary custom dat…

…a to receiver app on load.

packages/castable-video/castable-mixin.js

@@ -30,6 +30,7 @@ export const CastableMediaMixin = (superclass) =>
 
     #localState = { paused: false };
     #castOptions = getDefaultCastOptions();
+    #castCustomData;
     #remote;
 
     get remote() {
@@ -89,6 +90,7 @@ export const CastableMediaMixin = (superclass) =>
       if (!this.#castPlayer) return super.load();
 
       const mediaInfo = new chrome.cast.media.MediaInfo(this.castSrc, this.castContentType);
+      mediaInfo.customData = this.castCustomData;
 
       // Manually add text tracks with a `src` attribute.
       // M3U8's load text tracks in the receiver, handle these in the media loaded event.
@@ -221,6 +223,21 @@ export const CastableMediaMixin = (superclass) =>
       this.setAttribute('cast-stream-type', `${val}`);
     }
 
+    get castCustomData() {
+      return this.#castCustomData;
+    }
+
+    set castCustomData(val) {
+      console.log('setting castCustomData', val);
+      const valType = typeof val;
+      if (!['object', 'undefined'].includes(valType)) {
+        console.error(`castCustomData must be nullish or an object but value was of type ${valType}`);
+        return;
+      }
+
+      this.#castCustomData = val;
+    }
+
     get readyState() {
       if (this.#castPlayer) {
         switch (this.#castPlayer.playerState) {