Document the underlying types of the WKWindowFeatures rect properties
https://bugs.webkit.org/show_bug.cgi?id=134103

Reviewed by Dan Bernstein.

* UIProcess/API/Cocoa/WKWindowFeatures.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@170185 268f45cc-cd09-0410-ab3c-d52691b4dbfc