[content-visibility]: Make EnsureComputedStyle not dirty style.

When we do a EnsureComputedStyle in a display none subtree, we are
not in a style recalc but we still call SetRequestedState on a
display lock context. This means that we should not dirty style,
but rather rely on style adjustment for children to take the dirty
bit information.

The testcase for this is in
https://chromium-review.googlesource.com/c/chromium/src/+/2575815

which DCHECKs without this patch.

R=aleventhal@chromium.org

Bug: 1147481
Change-Id: Iaa24945f4ad44e73d0bf79ec757ad79b7081af9c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2579523
Reviewed-by: vmpstr <vmpstr@chromium.org>
Reviewed-by: Aaron Leventhal <aleventhal@chromium.org>
Commit-Queue: vmpstr <vmpstr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834832}