LayoutTests/webgl/max-active-contexts-webglcontextlost-prevent-default.html

<div id="result">PASS if the first context was lost due to creating too many WebGL contexts even though <code>preventDefault()</code> was called when a <code>webglcontextlost</code> event was dispatched.</div>
<script>
if (window.testRunner) {
    testRunner.waitUntilDone();
    testRunner.dumpAsText();
}

var maxNumberOfActiveContexts = 16;
var contexts = [];
for (var i = 0; i <= maxNumberOfActiveContexts; i++) {
    var canvas = document.createElement("canvas");
    canvas.addEventListener("webglcontextlost", function(event) {
        event.preventDefault();
        if (!contexts[0].isContextLost())
            document.getElementById("result").textContent = "FAIL";
        if (window.testRunner)
            testRunner.notifyDone();
    });
    contexts[i] = canvas.getContext("webgl");
}
</script>