DevTools: force a style recaclc before reporting final CSS coverage

Without this, taking a coverage report could be flaky if nothing
forced a style recalc. This can happen very often in headless mode.

Change-Id: If2bb596736f274d0aeceabec9ff7cf6076886eae
Reviewed-on: https://chromium-review.googlesource.com/c/1279293
Commit-Queue: Joel Einbinder <einbinder@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599782}
3 files changed