- Rename methods,
- Introduce flags for tokens to lookup IsKeyword and IsPropertyName
- Remove "contextual keyword" leftover code.
- Inline ParsePropertyName into ParsePropertyNameOrPrivatePropertyName
  since public is more likely than private.

Change-Id: Ib7633ef3c46889ecafc7a6c929029845bb8ef15c
Reviewed-on: https://chromium-review.googlesource.com/c/1357052
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57993}