Mark Vulkan Intel blink_web_tests slow

A few tests were timing out on Linux + Intel bots. However they
pass when the timeout is increased. Marking these tests as slow
on Linux to address this.

TBR=backer@chromium.org
Test=vulkan_native_blink_web_tests

Bug: 1018884
Change-Id: Ib2c0197e5f163ced2f76b7ba929f7c589f973de8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1900553Reviewed-by: Jonathan Ross <jonross@chromium.org>
Reviewed-by: Jonathan Backer <backer@chromium.org>
Commit-Queue: Jonathan Ross <jonross@chromium.org>
Cr-Commit-Position: refs/heads/master@{#713487}

third_party/blink/web_tests/SlowTests

@@ -667,4 +667,14 @@ crbug.com/984003 http/tests/virtual-scroller/find-element-66-10px.html [ Slow ]
 # Slow when using Vulkan.
 crbug.com/994331 compositing/lots-of-img-layers.html [ Slow ]
 
-crbug.com/1020379 http/tests/devtools/a11y-axe-core/performance/landing-page-a11y-test.js [ Slow ]
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+crbug.com/1020379 http/tests/devtools/a11y-axe-core/performance/landing-page-a11y-test.js [ Slow ]
+
+# Slow when using Vulkan on Linux with Intel
+crbug.com/1018884 [ Linux ] animations/change-keyframes.html [ Slow ]
+crbug.com/1018884 [ Linux ] animations/composition/word-spacing-composition.html [ Slow ]
+crbug.com/1018884 [ Linux ] animations/custom-properties/color-type-interpolation.html [ Slow ]
+crbug.com/1018884 [ Linux ] animations/direction-and-fill/animation-direction-alternate.html [ Slow ]
+crbug.com/1018884 [ Linux ] animations/events/compositor-start-event-timing.html [ Slow ]
+crbug.com/1018884 [ Linux ] animations/interpolation/webkit-mask-box-image-source-interpolation.html [ Slow ]
+crbug.com/1018884 [ Linux ] animations/prefixed/keyframes-unprefixed-01.html [ Slow ]
+crbug.com/1018884 [ Linux ] animations/responsive/animations-responsive-columnCount.html [ Slow ]
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