Mark synthetic_gestures/smooth-scroll-tiny-delta.html as timing out on fuchsia

TBR=bokan@chromium.org

Bug: 963739
Change-Id: I00a2908c78a81f788b5af458dc49bb96a79238d9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1616936Reviewed-by: Fergus Dall <sidereal@google.com>
Commit-Queue: Fergus Dall <sidereal@google.com>
Cr-Commit-Position: refs/heads/master@{#661244}

third_party/blink/web_tests/TestExpectations

@@ -5625,3 +5625,6 @@ crbug.com/963740 [ Win ] compositing/video-frame-size-change.html [ Pass Failure
 
 # Sheriff 2019-05-17
 crbug.com/964239 virtual/threaded/external/wpt/css/css-scroll-snap/scroll-margin.html [ Pass Failure ]
+
+# Sheriff 2019-05-20
+crbug.com/963739 [ Fuchsia ] synthetic_gestures/smooth-scroll-tiny-delta.html [ Pass Timeout ]
\ No newline at end of file