IDL compiler: constructor attributes

(Attributes named *Constructor.)
Pretty straightforward; some reordering for clarity.

BUG=239771
NOTRY=true

Review URL: https://codereview.chromium.org/36793003

git-svn-id: svn://svn.chromium.org/blink/trunk@160434 bbb929c8-8fbe-4397-9dbb-9b2b20218538