Chrome enum spec error

Changed the `<` and `>` to be `symbol`s instead of reserved words on `nonAnyType()`.

Found another difference between WebIDL and chrome IDLs. `enum` in the spec is defined as 

```
string	=	"[^"]*" 

[20]	Enum	→	"enum" identifier "{" EnumValueList "}" ";"
[21]	EnumValueList	→	string EnumValues
[22]	EnumValues	→	"," string EnumValues | ε
```
Example

```
enum MealType { "rice", "noodles", "other" , "with line
return"};
```

Chrome IDL uses an `identifier` for `enum` values

Example

```
// State of a window: normal, fullscreen, maximized, minimized.
enum State { normal, fullscreen, maximized, minimized };
``` 

This patch will bring the `web_idl_files_test.dart` to `96 PASSED, 0 FAILED, 6 ERRORS`