Rename drawSystemFocusRing() to drawFocusIfNeeded()

RESOLUTION: to change draw SystemFocusRing to drawFocusIfNeeded.

public discussion:
  http://www.w3.org/Bugs/Public/show_bug.cgi?id=23980
  http://www.w3.org/WAI/PF/HTML/wiki/Summary_of_2014-01-13_Meeting
  http://www.w3.org/2014/01/13-html-a11y-minutes.html#item02

other browsers:
  It has already been agreed or changed.
  http://bugzilla.mozilla.org/show_bug.cgi?id=959820 (Firefox)

BUG=354960

Review URL: https://codereview.chromium.org/208003003

git-svn-id: svn://svn.chromium.org/blink/trunk@169925 bbb929c8-8fbe-4397-9dbb-9b2b20218538