Revert "Mark paint/invalidation/window-resize slow"

This reverts commit 2ba4b0c6.

Reason for revert: new flakiness dashboard results show that the
tests are not actually slow. They are just occasionally stuck.

Original change's description:
> Mark paint/invalidation/window-resize slow
> 
> They occasionally timeout (1/10 ~ 1/20) on the bots, perhaps because of
> the multiple synchronized window resizes.
> 
> Bug: 919789
> Change-Id: I748b7362172b0ac407242e8236ae3ef937384f07
> Reviewed-on: https://chromium-review.googlesource.com/c/1484732
> Reviewed-by: Philip Rogers <pdr@chromium.org>
> Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#634900}

TBR=wangxianzhu@chromium.org,pdr@chromium.org

Change-Id: Ic9d1d868a23f62339e9c965d2a03b49fb2e5b531
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 919789
Reviewed-on: https://chromium-review.googlesource.com/c/1485020Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634943}

third_party/blink/web_tests/SlowTests

@@ -1576,6 +1576,4 @@ crbug.com/925600 external/wpt/webrtc-quic/RTCQuicStream.https.html [ Slow ]
 crbug.com/933550 external/wpt/service-workers/service-worker/interfaces-window.https.html [ Slow ]
 crbug.com/933550 external/wpt/webusb/idlharness.https.any.worker.html [ Slow ]
 
-crbug.com/919789 paint/invalidation/window-resize/ [ Slow ]
-
 crbug.com/927183 [ Mac10.13 ] external/wpt/html/semantics/embedded-content/the-iframe-element/iframe_sandbox_navigation_download_allow_downloads_without_user_activation.sub.tentative.html [ Slow ]

third_party/blink/web_tests/TestExpectations

@@ -5809,6 +5809,7 @@ crbug.com/719023 media_capabilities/encodingInfo-avc1.html [ Pass Failure ]
 
 # Sheriff 2019-01-07
 crbug.com/919492 [ Mac ] virtual/fractional_scrolling_threaded/fast/scrolling/overflow-scrollability.html [ Timeout Pass ]
+crbug.com/919504 paint/invalidation/window-resize/window-resize-vertical-writing-mode.html [ Timeout Pass ]
 crbug.com/919559 [ Win ] virtual/outofblink-cors/http/tests/fetch/window/thorough/redirect-loop.html [ Timeout Pass ]
 crbug.com/919587 [ Linux ] virtual/threaded/fast/idle-callback/idle_periods.html [ Pass Failure ]