Fix editing/spelling/spellcheck-editable-on-focus.html's flakiness

Due to asynchronous spell checker being on for the test
misspelling marks may appear after some time. The test checks
misspellings in different elements this is why it has to wait
until markers appear in *all* of them before checking
the pass conditions. However the test was not waiting
if markers appeared in at least one element.

BUG=None

Review URL: https://chromiumcodereview.appspot.com/23389005

git-svn-id: svn://svn.chromium.org/blink/trunk@156650 bbb929c8-8fbe-4397-9dbb-9b2b20218538