IDL compiler: SVGNames

Remaining: 14 => 12

Patch a bit long b/c need to pass |interface| down to scoped_name()
(for both getter and setter), but content otherwise simple.

BUG=239771
R=haraken, kouhei
NOTRY=true

Review URL: https://codereview.chromium.org/177143002

git-svn-id: svn://svn.chromium.org/blink/trunk@167669 bbb929c8-8fbe-4397-9dbb-9b2b20218538