Always initialize all members of WebWindowFeatures.

Prevents information leaks across the wire.

BUG=chromium:393981
R=jochen@chromium.org

Review URL: https://codereview.chromium.org/392973002

git-svn-id: svn://svn.chromium.org/blink/trunk@178199 bbb929c8-8fbe-4397-9dbb-9b2b20218538