Fix passing |this| as a bool to checkForSiblingStyleChanges

We should be passing true here, not |this|.

Review URL: https://codereview.chromium.org/240293008

git-svn-id: svn://svn.chromium.org/blink/trunk@171882 bbb929c8-8fbe-4397-9dbb-9b2b20218538