[css-flexbox] Migrate overflow-auto-resizes-correctly.html test to WPT

Partially migrate the contents of this test into the WPT-specific
directory, including only the checks that can be upstreamed and
leaving the parts that are Chromium-specific in the original test.

In addition, this CL also adapts the description of the original
Chromium-specific test to reflect what it actually does now after
having removed some parts. In the newly-added test, we also add
the relevant meta information i.e links to the relevant specs and
a test assertion describing its purpose.

Bug: 1063749
Change-Id: I57df80bf8a3c48dd94c70315a07d31715477a28b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2129537
Commit-Queue: Mario Sanchez Prada <mario@igalia.com>
Reviewed-by: David Grogan <dgrogan@chromium.org>
Reviewed-by: Robert Ma <robertma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#757780}
diff --git a/css/css-flexbox/overflow-auto-008.html b/css/css-flexbox/overflow-auto-008.html
new file mode 100644
index 0000000..03f843a
--- /dev/null
+++ b/css/css-flexbox/overflow-auto-008.html
@@ -0,0 +1,50 @@
+<!DOCTYPE html>
+<html>
+<title>CSS Flexbox: adding scrollbars with overflow: auto and flex-direction: column.</title>
+<link rel="help" href="https://drafts.csswg.org/css-overflow-3/#overflow-properties">
+<link rel="help" href="https://drafts.csswg.org/css-flexbox/#flex-direction-property">
+<link rel="help" href="https://crbug.com/512229">
+<meta name="assert" content="This test checks that, when a block inside a flexbox with flex-direction: column adds horizontal scrollbars due to overflow, the parent flexbox is still able to render its contents without overflowing."/>
+
+<style>
+.vflex {
+  display: flex;
+  flex-direction: column;
+  max-width: 200px;
+  margin: 10px 0 10px 0;
+}
+
+.hbox {
+  overflow-x: auto;
+  white-space: nowrap;
+}
+
+.rect {
+  min-height: 100px;
+  min-width: 100px;
+  background-color: green;
+  display: inline-block;
+}
+</style>
+
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<body>
+
+<div class="vflex">
+  <div class="hbox">
+    <div class="rect"></div>
+    <div class="rect"></div>
+  </div>
+</div>
+
+<script>
+var hbox = document.querySelector('.hbox');
+test(function() {
+  assert_equals(hbox.parentNode.clientHeight, hbox.parentNode.scrollHeight);
+  assert_equals(hbox.clientHeight, hbox.scrollHeight);
+}, 'hbox dimensions');
+</script>
+</body>
+</html>