This needs https://github.com/eqrion/cbindgen/pull/362, but I expect it to be
uncontroversial. I'll add a patch to this bug when it's merged to update it.
cbindgen historically didn't include these, but it turns out to be pretty useful
to generate constants for the style crate (since the binding crate is
`servo/ports/geckolib`).
An alternative is to get a completely different cbindgen-generated header for
these, but that seems a bit wasteful. This generates the constants with the
Style prefix (so we'll get `StyleMAX_GRID_LINE` for example), which is very
ugly. But we probably want to eventually stop using the Style prefix and use a
namespace instead, plus it's trivial to do `auto kMaxLine = StyleMAX_GRID_LINE`,
for example, so it's probably not a huge deal.
Another alternative would be to use associated consts, which _are_ generated by
cbindgen. Something like:
```
struct GridConstants([u8; 0]);
impl GridConstants {
const MAX_GRID_LINE: i32 = 10000;
}
```
Which would yield something like:
```
static const int32 StyleGridConstants_MAX_GRID_LINE = 10000;
```
I'm not sure if you find it preferrable, but I'm also happy to change it in a
follow-up to use this.
We need to fix a few manual C++ function signature definitions to match the C++
declaration.
Differential Revision: https://phabricator.services.mozilla.com/D35197
248b2ac829