third_party/WebKit/LayoutTests/fast/events/scroll-in-scaled-page-with-overflow-hidden.html

<style>
    html, body { margin:0; overflow: hidden; }
</style>
<script src="../../resources/js-test.js"></script>

<div>
  This tests that a usually overflow: hidden viewport should be scrollable when
  scaled. Otherwise, you can't get to content you would have been able to get to
  had you not been zoomed it.
</div>
<div id="console"></div>

<div style='font-size:40px; height: 1000px;'>
</div>

<script>
    (function() {
        if (!window.testRunner || !window.internals) {
            debug("This test only works in the test runner and requires window.internals.");
            return;
        }

        // Force a layout.
        document.body.offsetLeft;

        window.internals.setPageScaleFactor(2);

        // Note that with ScrollTopLeftInterop enabled, document.scrollingElement is
        // null because document.body is potentially scrollable (with overflow:hidden
        // the  box can still be scrolled programmatically).
        shouldBe("internals.visualViewportScrollY()", "0");

        if (window.eventSender) {
            eventSender.mouseMoveTo(100, 100);
            eventSender.mouseScrollBy(0, -5);
        }

        shouldBe("internals.visualViewportScrollY()", "200");
    })();
</script>