[css-properties-values-api] Move CSSSyntaxComponent to a separate file.

This is prerequisite for a subsequent CL.

R=futhark@chromium.org

Bug: 641877
Change-Id: Ifc8c1df0f80f9c18205b103e13ae90b5e2c63b2e
Reviewed-on: https://chromium-review.googlesource.com/c/1290980
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Anders Ruud <andruud@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601508}
5 files changed