IDL parser: Make MixinMember accept regular attribute

Before this CL, MixinMember did not accept regular attributes,
that are allowed in spec.
https://heycam.github.io/webidl/#index-prod-MixinMember

This CL clears the inconsistency.


Bug: 781257
Change-Id: I336bd92424e6bb2fb39be9a4087013b3d39bbc6a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1549295
Commit-Queue: Hitoshi Yoshida <peria@chromium.org>
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#647675}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: ae73c83f0f6deaeb06ad79b9286f54b0e83b9e79
2 files changed