Reduce exposure of PaintWorklet CSSPaintAPI

There are quite a few interfaces that are exposed under both
Window CSSTypedOM and PaintWorklet CSSPaintAPI. This CL limits the
exposure of CSSPaintAPI to CSSStyleValue and StylePropertyMapReadonly.

TBR=junov@chromium.org

Bug: 578252
Change-Id: Ia617df1ad17138a59fc9aeb214a376c9b8a5391b
Reviewed-on: https://chromium-review.googlesource.com/617307
Commit-Queue: Xida Chen <xidachen@chromium.org>
Reviewed-by: Xida Chen <xidachen@chromium.org>
Reviewed-by: meade_UTC10 <meade@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#496194}
6 files changed