[LayoutNG] testcase for codependent scrollbars

Just a testcase, because the bug cannot be fixed at this time. Aborted attempt to fix this is at: https://chromium-review.googlesource.com/c/chromium/src/+/1820177/4 Bug: 1007065 Change-Id: I44195ec77cc8b0924c81a567a9505e8a77f7d492 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1829878 Auto-Submit: Aleks Totic <atotic@chromium.org> Commit-Queue: Ian Kilpatrick <ikilpatrick@chromium.org> Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org> Cr-Commit-Position: refs/heads/master@{#701345}
web-platform-tests · Sep 30, 2019 · e2f3222 · e2f3222
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diff --git a/css/css-overflow/overflow-codependent-scrollbars.html b/css/css-overflow/overflow-codependent-scrollbars.html
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+<!DOCTYPE html>
+<link rel="author" href="mailto:atotic@google.com">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<link rel="help" href="https://www.w3.org/TR/css-overflow-3/#scrollable">
+<meta name="assert" content="What happens when appearance of one scrollbar triggers the other one?">
+<style>
+.container {
+  width: 100px;
+  height: 100px;
+  overflow: auto;
+  background: #DDD;
+  --too-big: 120px;
+  --slightly-smaller: 95px;
+}
+.target {
+  width: 120px;
+  height: 95px;
+  background: rgba(0,255,0,0.3);
+}
+</style>
+<!--  -->
+<div class="container">
+  <div class="target" style="width:var(--too-big);height:var(--slightly-smaller)" ></div>
+</div>
+<div class="container">
+  <div class="target" style="height:var(--too-big);width:var(--slightly-smaller)" ></div>
+</div>
+
+<script>
+test(() => {
+  Array.from(document.querySelectorAll(".container")).forEach( el => {
+    let verticalScrollbar = el.offsetWidth - el.clientWidth;
+    let horizontalScrollbar = el.offsetHeight - el.clientHeight;
+    assert_equals(verticalScrollbar, horizontalScrollbar, "both scrollbars are visible.");
+  });
+}, 'appearance of one scrollbar caused the other scrollbar to appear.');
+</script>