Fix Src= Build Issue after Bad Merge

Two changes around src= went in around the same time and they merged
poorly, resulting in a broken build. This change corrects that.

Issue #816
Issue #997

Change-Id: I1c84e56c06de0b80c11933144b453907f3e75786

lib/player.js

@@ -343,8 +343,8 @@ shaka.Player.prototype.destroy = async function() {
   // from interrupting our final move to the detached state.
   this.loadMode_ = shaka.Player.LoadMode.DESTROYED;
 
-  // Because we have set |isAlive_| to false, we can't call |detach|, so we
-  // must talk to the walker directly.
+  // Because we have set |loadMode_| to |DESTROYED| we can't call |detach|. We
+  // must talk to |this.walker_| directly.
   const events = this.walker_.startNewRoute((currentPayload) => {
     return {
       node: this.detachNode_,
@@ -728,10 +728,6 @@ shaka.Player.probeSupport = function() {
  */
 shaka.Player.prototype.attach = function(mediaElement,
                                          initializeMediaSource = true) {
-  goog.asserts.assert(
-      this.isAlive_,
-      'We should not be calling attach after destroy');
-
   // Do not allow the player to be used after |destroy| is called.
   if (this.loadMode_ == shaka.Player.LoadMode.DESTROYED) {
     return Promise.reject(this.createAbortLoadError_());
@@ -781,10 +777,6 @@ shaka.Player.prototype.attach = function(mediaElement,
  * @export
  */
 shaka.Player.prototype.detach = function() {
-  goog.asserts.assert(
-      this.isAlive_,
-      'We should not be calling detach after destroy');
-
   // Do not allow the player to be used after |destroy| is called.
   if (this.loadMode_ == shaka.Player.LoadMode.DESTROYED) {
     return Promise.reject(this.createAbortLoadError_());
@@ -821,10 +813,6 @@ shaka.Player.prototype.detach = function() {
  * @export
  */
 shaka.Player.prototype.unload = function(initializeMediaSource = true) {
-  goog.asserts.assert(
-      this.isAlive_,
-      'We should not be calling unload after destroy');
-
   // Do not allow the player to be used after |destroy| is called.
   if (this.loadMode_ == shaka.Player.LoadMode.DESTROYED) {
     return Promise.reject(this.createAbortLoadError_());
@@ -903,10 +891,6 @@ shaka.Player.prototype.unload = function(initializeMediaSource = true) {
  * @export
  */
 shaka.Player.prototype.load = function(assetUri, startTime, mimeType) {
-  goog.asserts.assert(
-      this.isAlive_,
-      'We should not be calling load after destroy');
-
   // Do not allow the player to be used after |destroy| is called.
   if (this.loadMode_ == shaka.Player.LoadMode.DESTROYED) {
     return Promise.reject(this.createAbortLoadError_());