Mark certain imagecapture/MediaStreamTrack tests as flaky

These tests are exhibiting flake on the main waterfall, as detailed on
the bugs listed below.

TBR=mcasas@chromium.org

Bug: 783301, 783800
Change-Id: I0770da4c7e7caf62ba65b3939f7417df7782ae36
Reviewed-on: https://chromium-review.googlesource.com/766189Reviewed-by: Colin Blundell <blundell@chromium.org>
Commit-Queue: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515942}

third_party/WebKit/LayoutTests/TestExpectations

@@ -3857,6 +3857,12 @@ crbug.com/781171 [ Android ] external/wpt/css/css-timing/step-timing-functions-o
 # Sheriff failures 2017-11-07
 crbug.com/782067 [ Mac10.10 Mac10.11 ] fast/css/no-recalc-on-no-op-inline-style-changes.html [ Pass Failure ]
 
+# Sheriff failures 2017-11-13
+crbug.com/783800 imagecapture/MediaStreamTrack-applyConstraints.html [ Pass Failure ]
+crbug.com/783800 imagecapture/MediaStreamTrack-applyConstraints-getSettings.html [ Pass Failure ]
+crbug.com/783301 imagecapture/MediaStreamTrack-getSettings.html [ Pass Failure ]
+crbug.com/783301 imagecapture/MediaStreamTrack-getCapabilities.html [ Pass Failure ]
+
 # Async Cookie API: hard to debug, also covered by working tests
 crbug.com/783229 external/wpt/async_cookies/cookie_store_tests.tentative.html [ Skip ]
 crbug.com/783229 external/wpt/async_cookies/cookie_store_tests.tentative.https.html [ Skip ]