Mark virtual/threaded Mac10.10 tests as slow.

Bug: 1065608
Change-Id: I06a99fbe1ad2d3168ed08503da6b13f7433e906d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2139751
Reviewed-by: Stephen Chenney <schenney@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#757042}

diff --git a/third_party/blink/web_tests/SlowTests b/third_party/blink/web_tests/SlowTests
index 40884876..4572c51 100644
--- a/third_party/blink/web_tests/SlowTests
+++ b/third_party/blink/web_tests/SlowTests

@@ -610,3 +610,11 @@
 crbug.com/937546 [ Win7 ] http/tests/security/xss-DENIED-cross-origin-stack-overflow.html [ Slow ]
 
 crbug.com/1066517 http/tests/websocket/workers/worker-reload.html [ Slow ]
+
+# Sometimes exceeds timeout on Mac10.10
+crbug.com/24182 [ Mac10.10 ] virtual/threaded/external/wpt/css/css-scroll-snap/snap-after-initial-layout/writing-mode-vertical-rl.html [ Slow ]
+crbug.com/24182 [ Mac10.10 ] virtual/threaded/external/wpt/css/css-animations/parsing/animation-shorthand.html [ Slow ]
+crbug.com/24182 [ Mac10.10 ] virtual/threaded/external/wpt/css/css-scroll-snap/snap-to-visible-areas-both.html [ Slow ]
+crbug.com/24182 [ Mac10.10 ] virtual/threaded/external/wpt/css/css-animations/KeyframeEffect-getKeyframes.tentative.html [ Slow ]
+crbug.com/24182 [ Mac10.10 ] virtual/threaded/external/wpt/css/css-scroll-snap/snap-after-initial-layout/writing-mode-horizontal-tb.html [ Slow ]
+crbug.com/24182 [ Mac10.10 ] virtual/threaded/external/wpt/css/css-animations/CSSAnimation-canceling.tentative.html [ Slow ]