Marking flaky tests

TBR: ericwilligers
No-Try: true
No-Presubmit: true
Bug: 769879
Change-Id: I217c445a716c687e8942dee2fbdc8a59b7cef55b
Reviewed-on: https://chromium-review.googlesource.com/690453
Commit-Queue: Daniel Murphy <dmurph@chromium.org>
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#505132}

third_party/WebKit/LayoutTests/TestExpectations

@@ -3650,7 +3650,8 @@ crbug.com/760543 [ Linux Release ] virtual/mojo-loading/http/tests/devtools/trac
 crbug.com/760543 [ Linux Release ] http/tests/devtools/tracing/timeline-paint/timeline-paint.html [ Pass Timeout ]
 crbug.com/760543 [ Linux Release ] virtual/mojo-loading/http/tests/devtools/tracing/timeline-paint/timeline-paint.html [ Pass Timeout ]
 
-crbug.com/761891 [ Win7 Debug ] virtual/threaded/animations/transition-and-animation-3.html [ Pass Failure Timeout ]
+crbug.com/761891 [ Win7 Linux Debug ] virtual/threaded/animations/transition-and-animation-3.html [ Pass Failure Timeout ]
+crbug.com/769879 [ Linux Debug ] virtual/threaded/transitions/transition-end-event-multiple-02.html [ Pass Failure ]
 crbug.com/769347 [ Mac ] fast/dom/inert/inert-node-is-uneditable.html [ Failure ]
 
 # Paint-timing tests timeout without threaded-compositing, so skip them.