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: svn://svn.chromium.org/blink/trunk@201574 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/LayoutTests/TestExpectations

@@ -730,6 +730,8 @@ crbug.com/302729 [ Android ] http/tests/media/media-source/mediasource-seek-beyo
 crbug.com/524160 [ Debug ] http/tests/media/media-source/mediasource-appendbuffer-quota-exceeded.html [ Timeout ]
 crbug.com/524160 [ Debug ] http/tests/media/media-source/mediasource-appendstream-quota-exceeded.html [ Timeout ]
 
+crbug.com/527152 http/tests/media/media-source/mediasource-duration.html [ Pass Crash ]
+
 crbug.com/517449 [ Android ] css3/images/optimize-contrast-image.html [ ImageOnlyFailure ]
 
 crbug.com/309675 compositing/gestures/gesture-tapHighlight-simple-longPress.html [ ImageOnlyFailure ]