Update window resize tests

- fixed two tests containing unrelated percentage width.
- added body margin:0 for some tests containing percentage lengths
  to make the results more readable after we optimize window resize
  repaint.
- made result of window-resize-viewport-percent.html platform
  independent.

BUG=258219

Review URL: https://codereview.chromium.org/275433007

git-svn-id: svn://svn.chromium.org/blink/trunk@173907 bbb929c8-8fbe-4397-9dbb-9b2b20218538