mark xss-DENIED-to-data-url tests as even more flaky.
mark xss-DENIED-to-data-url tests as even more flaky.

TBR=
BUG=372425,352464

Review URL: https://codereview.chromium.org/291063003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@174332 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs