Always initialize WindowFeatures.{x|y|width|height}

Based on WebKit r166072, which also updates a constructor that Blink
r171963 missed.

BUG=342591

Review URL: https://codereview.chromium.org/243583002

git-svn-id: svn://svn.chromium.org/blink/trunk@171984 bbb929c8-8fbe-4397-9dbb-9b2b20218538