Oilpan: Mark ContainerNode::ChildrenChange STACK_ALLOCATED.

And make Node* Member<>.

BUG=357163

Review URL: https://codereview.chromium.org/363383005

git-svn-id: svn://svn.chromium.org/blink/trunk@177508 bbb929c8-8fbe-4397-9dbb-9b2b20218538