IdNamespace is unique only within webrender instance

[sotaroikeda]

IdNamespace allocation is managed within webrender instance . Therefore there could be a case that different RenderApi could have same namespace_id between different webrender instances.

It causes the problem like Bug 1405241 on gecko since gecko assumes unique IdNamespace even between different webrender instances.

I am not sure if the problem should be addressed gecko side or webrender side.

[kvark]

I believe the end goal is to have a single WR instance anyway, that is managing multiple independent documents/scenes. In that case, WR will not need to have any built-in protection from multiple instances collision. However, in order to allow this to be patched on the Gecko side, WR does need to provide some way to make those IdNamespace different.

[glennw]

#1882 has landed.