Inline two methods seen in the N^2 shadowdom microbenchmark

I'm not sure how much either of these matter on real pages, but
they account for 2.8% and 1.8% of the profile each on this microbenchmark.

BUG=357479

Review URL: https://codereview.chromium.org/216453002

git-svn-id: svn://svn.chromium.org/blink/trunk@170378 bbb929c8-8fbe-4397-9dbb-9b2b20218538