feat: Add a way to listen to all events on a specific target

Change-Id: Ia7874430692edd289129dd38a1f59feee9fdc44b

lib/util/fake_event_target.js

@@ -49,6 +49,18 @@ shaka.util.FakeEventTarget = class {
     this.listeners_.push(type, listener);
   }
 
+  /**
+   * Add an event listener to this object that is invoked for all events types
+   * the object fires.
+   *
+   * @param {shaka.util.FakeEventTarget.ListenerType} listener The callback or
+   *   listener object to invoke.
+   * @exportInterface
+   */
+  listenToAllEvents(listener) {
+    this.addEventListener(shaka.util.FakeEventTarget.ALL_EVENTS_, listener);
+  }
+
   /**
    * Remove an event listener from this object.
    *
@@ -78,7 +90,12 @@ shaka.util.FakeEventTarget = class {
     goog.asserts.assert(event instanceof shaka.util.FakeEvent,
         'FakeEventTarget can only dispatch FakeEvents!');
 
-    const listeners = this.listeners_.get(event.type) || [];
+    let listeners = this.listeners_.get(event.type) || [];
+    const universalListeners =
+      this.listeners_.get(shaka.util.FakeEventTarget.ALL_EVENTS_);
+    if (universalListeners) {
+      listeners = listeners.concat(universalListeners);
+    }
 
     // Execute this event on listeners until the event has been stopped or we
     // run out of listeners.
@@ -120,3 +137,10 @@ shaka.util.FakeEventTarget = class {
  * @exportInterface
  */
 shaka.util.FakeEventTarget.ListenerType;
+
+
+/**
+ * @const {string}
+ * @private
+ */
+shaka.util.FakeEventTarget.ALL_EVENTS_ = 'All';