[whatwg] Concerns with <dialog>

[Brian Blakely]

Using Chrome Canary and http://demo.agektmr.com/dialog/ as a reference
implementation.

Are these spec concerns or Chromium implementation concerns?  Not
completely clear on this.

   1. When a modal dialog is active, the user can still scroll the
   underlying page.

   2. Even if the root element has overflow hidden, it should be possible
   to scroll the modal "layer" when a dialog escapes the boundaries of the
   viewport (or iframe).

   3. When the modal dialog's height changes, either due to CSS or content
   changes, the vertical position of the dialog should change (unless the
   height exceeds the viewport height).