Mark mediasource-duration.html as flaky crash
Mark mediasource-duration.html as flaky crash

At least on windows dbg and linux dbg, mediasource-duration.html has
started crashing since I landed the removal of short-circuiting
redundant seeks to same time in Chromium yesterday
(https://crrev.com/a609797f).

BUG=527152
TBR=philipj@opera.com
TEST=http/tests/media/media-source/mediasource-duration.html

Review URL: https://codereview.chromium.org/1308063006

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@201574 bbb929c8-8fbe-4397-9dbb-9b2b20218538

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk