Add new prerendering web API definitions.

PiperOrigin-RevId: 514438458

Author: Closure Team

externs/browser/html5.js

@@ -4655,6 +4655,12 @@ Document.prototype.fonts;
  */
 Document.prototype.currentScript;
 
+/**
+ * @see https://wicg.github.io/nav-speculation/prerendering.html#dom-document-prerendering
+ * @type {boolean}
+ */
+Document.prototype.prerendering;
+
 /**
  * Definition of ShadowRoot interface,
  * @see http://www.w3.org/TR/shadow-dom/#api-shadow-root

externs/browser/w3c_navigation_timing.js

@@ -122,6 +122,8 @@ function PerformanceNavigationTiming() {}
 /** @type {number} */ PerformanceNavigationTiming.prototype.loadEventEnd;
 /** @type {NavigationType} */ PerformanceNavigationTiming.prototype.type;
 /** @type {number} */ PerformanceNavigationTiming.prototype.redirectCount;
+// https://wicg.github.io/nav-speculation/prerendering.html#performance-navigation-timing-extension
+/** @type {number} */ PerformanceNavigationTiming.prototype.activationStart;
 
 /**
  * https://w3c.github.io/paint-timing/#sec-PerformancePaintTiming