 the overrideMimeType method is supported on the current
platform.
            </dd>
            <dt id="supportsProgressEvent" class="property">
                <span class="top-level-variable-type">bool</span>
                <a href="polymer_app_layout/HttpRequest/supportsProgressEvent.html">supportsProgressEvent</a>
            </dt>
            <dd>
                <div class="readable-writable">
        read-only
    </div>
    Checks to see if the Progress event is supported on the current platform.
