improve initiatorType

- 'fetch' for fetch() initiated requests
- 'preflight' for CORS-preflight requests
- 'other' to catch all other cases

closes #8

index.html

@@ -355,6 +355,9 @@ <h3>The <code>PerformanceResourceTiming</code> Interface</h3>
 <p>If the initiator is a CSS resource downloaded by the <code><a href="http://www.w3.org/TR/css-syntax-3/#consume-a-url-token">url()</a></code> syntax [[!CSS-SYNTAX-3]], such as <code>@import url()</code> or <code>background: url()</code>,
 on getting, the <code><a href="#widl-PerformanceResourceTiming-initiatorType">initiatorType</a></code> attribute MUST return the DOMString <code>"css"</code>.</p>
 <p>If the initiator is an XMLHttpRequest object [[!XMLHttpRequest]], on getting, the <code><a href="#widl-PerformanceResourceTiming-initiatorType">initiatorType</a></code> attribute MUST return the DOMString <code>"xmlhttprequest"</code>.</p>
+<p>If the initiator is the <a href="https://fetch.spec.whatwg.org/#dom-global-fetch">Fetch method</a> [[!Fetch]], on getting, the <code><a href="#widl-PerformanceResourceTiming-initiatorType">initiatorType</a></code> attribute MUST return the DOMString <code>"fetch"</code>.</p>
+<p>If the initiator is the <a href="https://fetch.spec.whatwg.org/#cors-preflight-fetch">CORS-preflight fetch</a> [[!Fetch]], on getting, the <code><a href="#widl-PerformanceResourceTiming-initiatorType">initiatorType</a></code> attribute MUST return the DOMString <code>"preflight"</code>.</p>
+<p>Otherwise, on getting, the initiatorType attribute MUST return the DOMString <code>"other"</code>.</p>
 </dd>
 
 <dt>readonly attribute DOMString nextHopProtocol</dt>