Use IDL default arguments for Window.confirm() and Window.prompt()

This doesn't change behavior.

BUG=258153

Review URL: https://codereview.chromium.org/368583004

git-svn-id: svn://svn.chromium.org/blink/trunk@177309 bbb929c8-8fbe-4397-9dbb-9b2b20218538
1 file changed
tree: 30b31fe3530836f8615990c472a6351f693b8921
  1. third_party/