Issue #1629 - Part 1: Implement basic logic in HTMLLinkElement.

So basically, I'm trying to adapt this to UXP:

https://bugzilla.mozilla.org/show_bug.cgi?id=1281135

The earliest source of difficulty while adapting Bug 1281135 to our codebase was simply getting the new ErrorResult flag added to the SetDisabled function to play nice with the SetMozDisabled function. At this point, the implementation can actually have a stylesheet be disabled by default but there are supposedly issues with alternate stylesheets.

At first I played around with the return type of SetMozDisabled to no avail, but I found another solution fairly quickly.

https://bugzilla.mozilla.org/show_bug.cgi?id=846972
https://bugzilla.mozilla.org/show_bug.cgi?id=1157898

Essentially, the way around the problem of the number of return arguments not matching up is to declare a local variable within SetMozDisabled called ErrorResult rv, and using that to store the return value of the ErrorResult argument from SetDisabled. After that, because ErrorCode was removed, you would return rv.StealNSResult() in order to report success or failure to any consumer that calls on SetMozDisabled.

dom/html/HTMLStyleElement.cpp

@@ -66,7 +66,7 @@ HTMLStyleElement::GetMozDisabled(bool* aDisabled)
 }
 
 bool
-HTMLStyleElement::Disabled()
+HTMLStyleElement::Disabled() const
 {
   StyleSheet* ss = GetSheet();
   return ss && ss->Disabled();