Replace on-stack HashSet<Node*> with WillBeHeapHashSet<RawPtrWillBeMember<Node>>

BUG=340522

Review URL: https://codereview.chromium.org/377143002

git-svn-id: svn://svn.chromium.org/blink/trunk@177718 bbb929c8-8fbe-4397-9dbb-9b2b20218538