Gardening: http/tests/svg/image-fetch-fail.svg is flaky

BUG=368560
TBR=jsbell
NOTRY=true

Review URL: https://codereview.chromium.org/264433004

git-svn-id: svn://svn.chromium.org/blink/trunk@172944 bbb929c8-8fbe-4397-9dbb-9b2b20218538