Improve 'MutationObserver' exception error messages.

This patch drops a static 'validateOptions' method from 'MutationObserver',
as it was only ever used in one place, and it would have been more work to
pass an error message around than to just inline the 4 checks into
'MutationObserver::observe'.

BUG=270033
R=jochen@chromium.org

Review URL: https://codereview.chromium.org/26801002

git-svn-id: svn://svn.chromium.org/blink/trunk@159333 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Mark tests that need to be rebaselined now that http://crrev.com/26133002 has landed

This marks effect-reference-hidpi-hw.html and effect-reference-zoom-hw.html
for rebaselining. These tests need to be rebaselined because of Chromium
CL http://crrev.com/26133002.

TBR=senorblanco@chromium.org
BUG=181613

Review URL: https://codereview.chromium.org/26843002

git-svn-id: svn://svn.chromium.org/blink/trunk@159334 bbb929c8-8fbe-4397-9dbb-9b2b20218538