Lots of malformed WebIDL files

A lot of the WebIDL files are malformed in the same way: they have an interface declaration like so:

```webidl
interface nameofinterface;
```

which is not valid WebIDL. The valid equivalent is

```webidl
interface nameofinterface {};
```

We could either change all the webidl files to be correct, or adapt the parser to handle the above form.