Properly test !CSSPaintAPIArguments in CSSPaintValueTest

Previously all the tests assumed that CSSPaintAPIArguments was on, which
was covering up a bug where OffMainThreadCSSPaint would create a
deferred image even though the generator wasn't ready (because
ParseInputArguments would pass due to !CSSPaintAPIArguments). This CL
fixes the tests to actually test all combinations, and fixes the bug by
extracting the generator-ready check outside of ParseInputArguments.

Bug: None
Change-Id: I6789cf24b7efa6035a88990082a857f24ccafbb4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1689953
Reviewed-by: Xida Chen <xidachen@chromium.org>
Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#675214}
2 files changed