The bulk of this commit was generated by running:
run-clang-tidy.py \
-checks='-*,llvm-namespace-comment' \
-header-filter=^/.../mozilla-central/.* \
-fix
Destroying large arrays of css::Rules during page teardown can take
multiple milliseconds in incremental CC. To reduce CC pauses, this
patch introduces a new class nsIncrementalClearCOMRuleArray that uses
the deferred finalizer to incrementally destroy these rule arrays.