drop optional on workerStart

index.html

@@ -357,7 +357,7 @@ <h3>The <code>PerformanceResourceTiming</code> Interface</h3>
 </dd>
 
 <dt>readonly attribute DOMHighResTimeStamp workerStart</dt>
-<dd>This attribute is optional. User agents that don't have this attribute available must set it as undefined. When this attribute is supported and the current browsing or worker context's have an <a href="http://www.w3.org/TR/service-workers/#dfn-containing-service-worker-registration">active worker</a> ([[!SERVICE-WORKERS]]), it MUST return the time immediately before the user agent <a href="http://www.w3.org/TR/service-workers/#service-worker-concept">runs the worker</a> required to service the request, or if the worker is available, the time immediately before the user agent <a href="http://www.w3.org/TR/service-workers/#on-fetch-request-algorithm">fires an event named `fetch`</a> at the <a href="http://www.w3.org/TR/service-workers/#dfn-active-worker">active worker</a>. Otherwise, if there is no active worker this attribute MUST return zero.</dd>
+<dd>If the current browsing or worker context's have an <a href="http://www.w3.org/TR/service-workers/#dfn-containing-service-worker-registration">active worker</a> ([[!SERVICE-WORKERS]]), this atribute MUST return the time immediately before the user agent <a href="http://www.w3.org/TR/service-workers/#service-worker-concept">runs the worker</a> required to service the request, or if the worker is available, the time immediately before the user agent <a href="http://www.w3.org/TR/service-workers/#on-fetch-request-algorithm">fires an event named `fetch`</a> at the <a href="http://www.w3.org/TR/service-workers/#dfn-active-worker">active worker</a>. Otherwise, if there is no active worker this attribute MUST return zero.</dd>
 
 <dt>readonly attribute DOMHighResTimeStamp redirectStart</dt>
 <dd>
@@ -696,7 +696,7 @@ <h3>Processing Model</h3>
       <li>Record the initiator of the resource in <a href="#widl-PerformanceResourceTiming-initiatorType">initiatorType</a>.
       </li>
 
-      <li>Record the <a href="http://www.w3.org/TR/html5/infrastructure.html#resolve-a-url">resolved URL</a> of the requested resource in <a href="#widl-PerformanceResourceTiming-name">name</a>. If there is an <a href="http://www.w3.org/TR/service-workers/#dfn-containing-service-worker-registration">active worker</a> ([[!SERVICE-WORKERS]]) matching the current browsing or worker context's, immediately before the user agent <a href="http://www.w3.org/TR/service-workers/#service-worker-concept">runs the worker</a> record the time as <a href="#widl-PerformanceResourceTiming-workerStart">workerStart</a>, or if the worker is available, immediately before the <a href="http://www.w3.org/TR/service-workers/#on-fetch-request-algorithm">event named `fetch` is fired</a> at the active worker record the time as <a href="#widl-PerformanceResourceTiming-workerStart">workerStart</a>. Otherwise, if <a href="#widl-PerformanceResourceTiming-workerStart">workerStart</a> attribute is supported but there is no matching <a href="http://www.w3.org/TR/service-workers/#dfn-service-worker-registration">service worker registration</a>, set <a href="#widl-PerformanceResourceTiming-workerStart">workerStart</a> value to zero.</li>
+      <li>Record the <a href="http://www.w3.org/TR/html5/infrastructure.html#resolve-a-url">resolved URL</a> of the requested resource in <a href="#widl-PerformanceResourceTiming-name">name</a>. If there is an <a href="http://www.w3.org/TR/service-workers/#dfn-containing-service-worker-registration">active worker</a> ([[!SERVICE-WORKERS]]) matching the current browsing or worker context's, immediately before the user agent <a href="http://www.w3.org/TR/service-workers/#service-worker-concept">runs the worker</a> record the time as <a href="#widl-PerformanceResourceTiming-workerStart">workerStart</a>, or if the worker is already available, immediately before the <a href="http://www.w3.org/TR/service-workers/#on-fetch-request-algorithm">event named `fetch` is fired</a> at the active worker record the time as <a href="#widl-PerformanceResourceTiming-workerStart">workerStart</a>. Otherwise, if there is no matching <a href="http://www.w3.org/TR/service-workers/#dfn-service-worker-registration">service worker registration</a>, set <a href="#widl-PerformanceResourceTiming-workerStart">workerStart</a> value to zero.</li>
 
       <li id="step-fetch-start">Immediately before a user agent starts the <a href="http://www.w3.org/TR/html5/infrastructure.html#fetch" title='fetch'>fetching process</a>, record the current time as <a href="#widl-PerformanceResourceTiming-fetchStart">fetchStart</a>. Let <a href="#widl-PerformanceResourceTiming-domainLookupStart">domainLookupStart</a>, <a href="#widl-PerformanceResourceTiming-domainLookupEnd">domainLookupEnd</a>, <a href="#widl-PerformanceResourceTiming-connectStart">connectStart</a> and <a href="#widl-PerformanceResourceTiming-connectEnd">connectEnd</a> be the same value as <a href="#widl-PerformanceResourceTiming-fetchStart">fetchStart</a>.</li>