IDL compiler: sync Python to r165630

Python side to:
Rename [GenerateVisitDOMWrapper] to [SetWrapperReferenceFrom]
https://codereview.chromium.org/143463013

Also minor refactoring and rectification of names in:
ext_attributes_node_to_extended_attributes

BUG=239771
TBR=haraken
NOTRY=true

Review URL: https://codereview.chromium.org/139353004

git-svn-id: svn://svn.chromium.org/blink/trunk@165685 bbb929c8-8fbe-4397-9dbb-9b2b20218538