Revert "Mark media/video-seeking.html as flaky"
Revert "Mark media/video-seeking.html as flaky"

This reverts commit 79544d9f0d63b9b22c7e8dd6e8f05cd437215315. The cause of the
failing test has been fixed in Chromium.

BUG=435342

Review URL: https://codereview.chromium.org/770723003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@186286 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