Syntax errors from bad Javascript in an onclick attribute string never reach onerror

[pshaughn]

This is in WPT html/webappapis/scripting/processing-model-2/compile-error-in-attribute.html. The situation is somwhat similar to #25194 but when the syntax error is in an onclick attribute string, instead of a string argument to setTimeout/setInterval, onerror never even gets called in the first place.

[pshaughn]

Looking closer at the code and spec now to see what step should throw and whether adding the throw would be an easy change or a hard one.

[pshaughn]

There's a FIXME #13152 in there; this is a piece of a bigger problem and basically a duplicate issue.