Remove first argument for shoudCreateCustomElement()

After https://codereview.chromium.org/2252003002
(Change custom element state in documents without browsing context),
the first argument (document) is not necessary for
CustomElement::shouldCreateCustomElement().

This is clean-up only and no functional change.

BUG=594918

Review-Url: https://codereview.chromium.org/2258023003
Cr-Commit-Position: refs/heads/master@{#413096}
4 files changed