IDL compiler: info.GetReturnValue().Set => v8SetReturnValue

Fixes v. outdated function calls, per request of haraken@:
https://codereview.chromium.org/100473006/#msg2

Review URL: https://codereview.chromium.org/98673005

git-svn-id: svn://svn.chromium.org/blink/trunk@163246 bbb929c8-8fbe-4397-9dbb-9b2b20218538