Add test for crbug.com/1138917

Bug: 1138917
Change-Id: I406730e0d673ac7f58cc9309f8b95141c9623f60
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2476156
Auto-Submit: Fredrik Söderquist <fs@opera.com>
Commit-Queue: Stephen Chenney <schenney@chromium.org>
Reviewed-by: Stephen Chenney <schenney@chromium.org>
Cr-Commit-Position: refs/heads/master@{#817597}

third_party/blink/web_tests/external/wpt/css/css-masking/clip-path-svg-content/clip-path-no-content-005.svg

+<svg xmlns="http://www.w3.org/2000/svg" xmlns:h="http://www.w3.org/1999/xhtml"
+     class="reftest-wait">
+  <title>Removing a clip-path attribute pointing to an empty &#x3c;clipPath&#x3e;</title>
+  <h:link rel="help" href="https://drafts.fxtf.org/css-masking-1/#ClipPathElement"/>
+  <h:link rel="match" href="reference/clip-path-square-003-ref.svg"/>
+  <h:script src="/common/reftest-wait.js"/>
+  <h:script src="/common/rendering-utils.js"/>
+
+  <clipPath id="empty"/>
+  <g clip-path='url("#empty")'>
+    <rect width="200" height="200" fill="green"/>
+  </g>
+  <script>
+    waitForAtLeastOneFrame().then(() => {
+      document.querySelector('svg > g').removeAttribute('clip-path');
+      takeScreenshot();
+    });
+  </script>
+</svg>