Gardening: form-method-dialog.html is no longer flaky

BUG=310330
TBR=jsbell

Review URL: https://codereview.chromium.org/39283002

git-svn-id: svn://svn.chromium.org/blink/trunk@160411 bbb929c8-8fbe-4397-9dbb-9b2b20218538