Increase timeout for wpt...CSS2...line-height-interpolation.html

This test was running with an average speed close to its timeout and
was occasionally exceeding it, causing flakes. Marking it as slow as
per wpt guidelines.

Bug: 1073460
Change-Id: I2028d64ed727242ec3873c5172a08ecebbc45a73
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2163395
Commit-Queue: George Steel <gtsteel@chromium.org>
Reviewed-by: Kevin Ellis <kevers@chromium.org>
Cr-Commit-Position: refs/heads/master@{#762061}

third_party/blink/web_tests/TestExpectations

@@ -6729,7 +6729,6 @@ crbug.com/1073247 external/wpt/webaudio/the-audio-api/the-convolvernode-interfac
 # Sheriff 2020-04-22
 # Flaky test.
 crbug.com/1073431 http/tests/streams/transferable/readable-stream.html [ Pass Failure ]
-crbug.com/1073460 external/wpt/css/CSS2/linebox/animations/line-height-interpolation.html [ Pass Timeout ]
 crbug.com/1073505 [ Mac10.13 ] external/wpt/html/semantics/scripting-1/the-script-element/moving-between-documents/* [ Pass Failure ]
 crbug.com/1073505 [ Mac10.13 ] virtual/web-components-v0-disabled/external/wpt/html/semantics/scripting-1/the-script-element/moving-between-documents/* [ Pass Failure ]
 crbug.com/1073505 [ Mac10.13 ] external/wpt/html/semantics/scripting-1/the-script-element/moving-between-documents/before-prepare-iframe-success-external-module.html [ Pass Failure ]

third_party/blink/web_tests/external/wpt/css/CSS2/linebox/animations/line-height-interpolation.html

@@ -3,6 +3,7 @@
 <title>line-height interpolation</title>
 <link rel="help" href="https://www.w3.org/TR/CSS2/visudet.html#propdef-line-height">
 <meta name="assert" content="line-height supports animation by computation">
+<meta name="timeout" content="long">
 
 <script src="/resources/testharness.js"></script>
 <script src="/resources/testharnessreport.js"></script>