Oilpan: Replace RefPtrs and raw pointers to Node and its subclasses in core/frame and core/page with Oilpan transition types.

Also, this CL replaces SmartClipData::m_node with m_isEmpty.

BUG=357163

Review URL: https://codereview.chromium.org/310353003

git-svn-id: svn://svn.chromium.org/blink/trunk@175445 bbb929c8-8fbe-4397-9dbb-9b2b20218538