Move CFG management out of NodeTraversal and into common callback base class (NodeTraversal.AbstractCfgCallback).
Add externs for maps api v3.50.
Modifications to make the missing property and property creations checks on union stricter. A property must be known on all members of a union (excluding null or undefined). Previously, existance on any member of the union was sufficient.
Fix incorrect optimization that inlines super.x() to super.x