chromium/third_party/blink/web_tests/compositing/contents-opaque/background-color.html

<html>
    <head>
        <style type="text/css">
            .box {
                width: 100px;
                height: 100px;
            }
            .opaque {
                background-color: green;
            }
            .translucent {
                background-color: rgba(0, 255, 0, 0.5);
            }
            .composited {
                will-change: transform;
            }
        </style>
        <script type="text/javascript">
            if (window.testRunner)
                testRunner.dumpAsText();

            function doTest() {
                if (window.testRunner && window.internals)
                    document.getElementById('layertree').innerText = internals.layerTreeAsText(document);
            }
            window.addEventListener('load', doTest, false);
        </script>
    </head>
    <body>
        <!-- Box with transparent background. -->
        <!-- GraphicsLayer::contentsOpaque for this box should be false. -->
        <div class="box composited"></div>
        <!-- Box with translucent background color. -->
        <!-- GraphicsLayer::contentsOpaque for this box should be false. -->
        <div class="box translucent composited"></div>
        <!-- Box with opaque background color. -->
        <!-- GraphicsLayer::contentsOpaque for this box should be true. -->
        <div class="box opaque composited"></div>

        <pre id="layertree"></pre>
    </body>
</html>