Pull up a subset of CanvasRenderingContext2D into BaseRenderingContext2D.

This will allow an additional sub-class of BaseRC2D called PaintRC2D.
BaseRC2D contains the subset of APIs needed for PaintRC2D.

See: https://drafts.css-houdini.org/css-paint-api/#paintrenderingcontext2d

This is a reland of: https://codereview.chromium.org/1710633002

BUG=578252

Review URL: https://codereview.chromium.org/1739553002

Cr-Commit-Position: refs/heads/master@{#377628}
5 files changed