Fix CastUtils.serialize handling of errors.

Beforehand, we stripped out all objects variables in events when
serializing. This was intended to remove complicated DOM objects, and
prevent the error messages from containing large amounts of unnecessary
information. However, this also caused the cast receiver to strip away
the detail variable in error events, thus removing all useful
information from the error event.
This adds a special exception to serialize for the contents of the
'detail' variable.

Issue #1065

Change-Id: Ie291e317cc6e856af20af5df57ecf3b5c81ec8bd

lib/cast/cast_utils.js

@@ -250,6 +250,11 @@ shaka.cast.CastUtils.serialize = function(thing) {
       for (var eventKey in value) {
         var eventValue = value[eventKey];
         if (eventValue && typeof eventValue == 'object') {
+          if (eventKey == 'detail') {
+            // Keep the detail value, because it contains important information
+            // for diagnosing errors.
+            simpleEvent[eventKey] = eventValue;
+          }
           // Strip out non-null object types because they are complex and we
           // don't need them.
         } else if (eventKey in Event) {