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- currently when CSS.supports is called it does not pass in the
  ExecutionContext to the css parser context, hence it does not support
  Origin Trial enabled properties/values.

- This changeset added plumbing to pass in the top level document to
  CSSParserContext which we extracted from ExecutionContext.

- Repurposed one of the ParseValue overload and change all its callsite
  to pass in ExecutionContext, they were previously passing in
  ExecutionContext->GetSecureContext()

- CSSParserContext used in support parsing are constructed using the
  document if the execution context belongs to one. We then override
  the parser mode to kHTMLStandardMode as quirks mode values must not
  be supported in CSS.supports method according to
  https://quirks.spec.whatwg.org/#css
  This is also in line with current behaviours before document
  is added to the context.

- Added virtual test that checks for CSS.supports(condition) and
  CSS.supports(property, value)

Bug: 1134237
Change-Id: I4c1b3cd2707f3ce5495ee298a909e3f42946fc09
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2477014Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Reviewed-by: Jason Chase <chasej@chromium.org>
Commit-Queue: Rodney Ding <rodneyding@google.com>
Cr-Commit-Position: refs/heads/master@{#821909}