Remove buffering of styles?

I think insertRule might give us good performance so that we could remove style buffering. This would reduce complexity and make the abstraction less leaky.

Profiling should be done before shipping this.

No files or tests are named. Start by profiling the existing style buffering and the insertRule path, then determine whether the profiling supports removing buffering without losing performance. Done means the proposed simplification is validated by profiling and the abstraction is less complex.

Written by the indexing model from the issue text.