Fix IE11 Fullscreen button disappearance

In IE11, the fullscreen button in the controls UI disappears after
clicking 'Load'. This is because the classList toggle method is not
fully supported for IE11, so the 'casting' class is added to the
controls div every time. Fixing by using add and remove instead of
toggle.

Closes #787.

Change-Id: I9c4f2cfdc32d1ed11e3a4b5b86e885bd8c10db3d

build/conformance.textproto

@@ -83,6 +83,14 @@ requirement: {
 }
 
 
+#Disallow classList toggle.
+requirement: {
+  type: BANNED_PROPERTY_CALL
+  value: 'DOMTokenList.prototype.toggle'
+  error_message: 'classList toggle is not supported in IE11'
+}
+
+
 # Disallow ES6 methods.
 requirement: {
   type: BANNED_PROPERTY

demo/controls.js

@@ -550,7 +550,11 @@ ShakaControls.prototype.onCastStatusChange_ = function(event) {
       isCasting ? 'inherit' : 'none';
   this.castReceiverName_.textContent =
       isCasting ? 'Casting to ' + this.castProxy_.receiverName() : '';
-  this.controls_.classList.toggle('casting', this.castProxy_.isCasting());
+  if (this.castProxy_.isCasting()) {
+    this.controls_.classList.add('casting');
+  } else {
+    this.controls_.classList.remove('casting');
+  }
 };