feat(ui): Add ability to build UI without cast (#4781)

With this, if you build Shaka Player with "-@cast", the UI will contain
a dummy cast proxy that does not require the full cast system.

build/build.py

@@ -185,6 +185,13 @@ class Build(object):
         return True
     return False
 
+  def has_cast(self):
+    """Returns True if the cast system is in the build."""
+    for path in self.include:
+      if 'cast' in path.split(os.path.sep):
+        return True
+    return False
+
   def generate_localizations(self, locales, force):
     localizations = compiler.GenerateLocalizations(locales)
     localizations.generate(force)
@@ -275,6 +282,10 @@ class Build(object):
       return False
     if self.has_ui():
       self.generate_localizations(locales, force)
+      # So that the UI will correctly build if the cast is disabled, add the
+      # dummy cast proxy.
+      if not self.has_cast():
+        self.include.add(os.path.abspath('conditional/dummy_cast_proxy.js'))
 
     if is_debug:
       name += '.debug'

conditional/dummy_cast_proxy.js

@@ -0,0 +1,120 @@
+/*! @license
+ * Shaka Player
+ * Copyright 2016 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+goog.provide('shaka.cast.CastProxy');
+
+goog.require('shaka.Player');
+goog.require('shaka.util.FakeEventTarget');
+goog.require('shaka.util.IDestroyable');
+
+/**
+ * @summary A dummy version of the cast proxy. Meant to allow Shaka Player to
+ * build the UI without the cast system.
+ *
+ * @implements {shaka.util.IDestroyable}
+ * @export
+ */
+shaka.cast.CastProxy = class extends shaka.util.FakeEventTarget {
+  /**
+   * @param {!HTMLMediaElement} video
+   * @param {!shaka.Player} player
+   * @param {string} receiverAppId
+   * @param {boolean} androidReceiverCompatible
+   */
+  constructor(video, player, receiverAppId, androidReceiverCompatible = false) {
+    super();
+
+    /** @private {!HTMLMediaElement} */
+    this.video_ = video;
+
+    /** @private {!shaka.Player} */
+    this.player_ = player;
+  }
+
+  /**
+   * @param {boolean=} forceDisconnect
+   * @override
+   * @export
+   */
+  async destroy(forceDisconnect) {
+    await this.player_.destroy();
+    super.release();
+  }
+
+  /**
+   * @return {!HTMLMediaElement}
+   * @export
+   */
+  getVideo() {
+    return this.video_;
+  }
+
+  /**
+   * @return {!shaka.Player}
+   * @export
+   */
+  getPlayer() {
+    return this.player_;
+  }
+
+  /**
+   * @return {boolean}
+   * @export
+   */
+  canCast() {
+    return false;
+  }
+
+  /**
+   * @return {boolean}
+   * @export
+   */
+  isCasting() {
+    return false;
+  }
+
+  /**
+   * @return {string}
+   * @export
+   */
+  receiverName() {
+    return 'dummy';
+  }
+
+  /**
+   * @return {!Promise}
+   * @export
+   */
+  async cast() {
+    await Promise.resolve();
+  }
+
+  /**
+   * @param {Object} appData
+   * @export
+   */
+  setAppData(appData) {}
+
+  /**
+   * @export
+   */
+  suggestDisconnect() {}
+
+  /**
+   * @export
+   */
+  forceDisconnect() {}
+
+
+  /**
+   * @param {string} newAppId
+   * @param {boolean=} newCastAndroidReceiver
+   * @export
+   */
+  async changeReceiverId(newAppId, newCastAndroidReceiver = false) {
+    await Promise.resolve();
+  }
+};