[css-properties-values-api] Compute <time> values to seconds.

The CSSPrimitiveValue::IsTime function (non-static) did for some reason
use GetType() instead of TypeWithCalcResolved(), even though both
ComputeSeconds() and TypeWithCalcResolved() do seemingly handle calculated
time correctly.

R=futhark@chromium.org

Bug: 641877
Change-Id: I0e927265f01855b8262ed9201df9eae647171b8d
Reviewed-on: https://chromium-review.googlesource.com/c/1304481
Commit-Queue: Anders Ruud <andruud@chromium.org>
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603832}
5 files changed