ExtensionToolbarModelTest.ReorderAndReinsert is flaky on Blink Mac canaries

BUG=166580
TBR=finnur@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/34623017

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230459 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230459