Bug 858288 - set sandbox to null in switchToFrame, r=jgriffin
Bug 858203 - mark more reftests as needs-focus; r=dholbert

1. Start headless X server.  Start basic window manager on it.
2. Run reftests with said X server.  Take note of failing tests.
3. Disable all reftests that need focus:

   find $topsrcdir -name '*.list' | xargs sed -i -e '/needs-focus/s/^/#/'

4. Make reftest.js:Focus never focus the window and always return true.
5. Start reftests with said X server again.  Once the tests begin
   running, start a xterm on the same X server.  The window manager will
   focus this xterm and will not return focus to the browser.
6. Compare now-failing tests with baseline.  Mark all such tests as
   needs-focus.

Comments on specific tests:

editor/reftests/
- spellcheck-input-ref.html and spellcheck-textarea-ref.html focus
  input elements and don't work right without the window having focus.
- spellcheck-hyphen-invalid-ref.html and
  spellcheck-hyphen-multiple-invalid-ref.html use @autofocus on
  textarea.
- 674212-spellcheck.html, 338427-2.html, and
  462758-grabbers-resizers.html all wait for onfocus for div elements.

layout/reftests/bugs/
- 652301-1b.html focuses a bogus element with an onfocus handler.

layout/reftests/selection/
- pseudo-element-of-native-anonymous-ref.html .select()s an <input>.