Mark external/wpt/css/css-fonts/font-display/font-display.html Slow

It takes at least 5 seconds. Marking it as SLOW to ensure that it runs
with an increased timeout.

NoTry: True
Bug: 816026
Change-Id: Ie6923678e945b05def57f93647ae69a97190da86
Reviewed-on: https://chromium-review.googlesource.com/961922
Commit-Queue: Kunihiko Sakamoto <ksakamoto@chromium.org>
Reviewed-by: Takashi Toyoshima <toyoshim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543028}

third_party/WebKit/LayoutTests/SlowTests

@@ -479,7 +479,9 @@ crbug.com/779366 fast/shapes/crash-allocating-very-large-raster-shape.html [ Slo
 
 crbug.com/787971 external/wpt/WebCryptoAPI/wrapKey_unwrapKey/wrapKey_unwrapKey.https.worker.html [ Slow ]
 
+# These font-display tests are slow as they test web fonts behavior around the 3-seconds timeout.
 crbug.com/564109 http/tests/webfont/font-display-intervention.html [ Slow ]
+crbug.com/816026 external/wpt/css/css-fonts/font-display/font-display.html [ Slow ]
 
 # This test has many test cases and each case requires a gesture scroll with pauses in between.
 crbug.com/765326 virtual/scroll_customization/fast/scroll-behavior/scroll-customization/scroll-customization-property.html [ Slow ]

third_party/WebKit/LayoutTests/TestExpectations

@@ -3316,9 +3316,6 @@ crbug.com/814889 [ Debug ] idle-callback/test-runner-run-idle-tasks.html [ Timeo
 crbug.com/814953 fast/replaced/no-focus-ring-iframe.html [ Failure Pass ]
 crbug.com/814964 virtual/gpu-rasterization/images/color-profile-border-radius.html [ Failure Pass ]
 
-# Sheriff failures 2018-02-26
-crbug.com/816026 external/wpt/css/css-fonts/font-display/font-display.html [ Failure Pass Timeout ]
-
 # MSAN
 crbug.com/813547 [ Linux ] webaudio/BiquadFilter/tail-time-lowpass.html [ Pass Failure ]