[css-properties-values-api] Validate generate_property argument.

This prevents silently dropping invalid arguments. For example, the
following currently generates a non-inherited property:

  let name = generate_property(syntax: '<length>', inherited: true);

This is because 'inherited' is not an option for CSS.registerProperty (the
actual option is 'inherits').

With this change, an exception is thrown if unknown options are provided.

R=futhark@chromium.org

Bug: 641877
Change-Id: I7b639651c331aa705416db95a3de751353648031
Reviewed-on: https://chromium-review.googlesource.com/c/1304522
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Anders Ruud <andruud@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603862}
2 files changed