Make handle_potential_webgl_error more ergonomic

[jdm]

We have a macro called handle_potential_webgl_error which takes a return value as the third argument. In the case where a caller has a void return type, we use it like handle_potential_webgl_error(a, b, ()) which I find ugly. We can extend the macro to have a second variant that only takes two arguments and passes the () argument internally, like http://mxr.mozilla.org/servo/source/components/script/dom/macros.rs#6 .

Code: components/script/dom/webglrenderingcontext.rs

[wilcus]

I take this :).

[jdm]

Great!

[wilcus]

@jdm When you pass None as the third argument do you not mean it's () ?

[jdm]

No, None is used for methods that return Option<T>. The () is used for methods that have no return type at all.