Add render-blocking boolean to fetch timing info

This supports the addition of a render blocking status field to PerformanceResourceTiming. Further details are available at w3c/resource-timing#327.

Author: abinpaul1

fetch.bs

@@ -289,6 +289,8 @@ following <a for=struct>items</a>: [[RESOURCE-TIMING]] [[NAVIGATION-TIMING]]
 
  <dt><dfn export for="fetch timing info">server-timing headers</dfn> (default « »)
  <dd>A <a for=/>list</a> of strings.
+ <dt><dfn export for="fetch timing info">render-blocking</dfn> (default false)
+ <dd>A boolean.
 </dl>
 
 <p>A <dfn export>response body info</dfn> is a <a for=/>struct</a> used to maintain
@@ -3888,7 +3890,9 @@ the request.
  <li><p>Let <var>timingInfo</var> be a new <a for=/>fetch timing info</a> whose
  <a for="fetch timing info">start time</a> and
  <a for="fetch timing info">post-redirect start time</a> are the
- <a for=/>coarsened shared current time</a> given <var>crossOriginIsolatedCapability</var>.
+ <a for=/>coarsened shared current time</a> given <var>crossOriginIsolatedCapability</var>, and
+ <a for="fetch timing info">render-blocking</a> is set to <var>request</var>'s
+ <a for=request>render-blocking</a>.
 
  <li><p>Let <var>fetchParams</var> be a new <a for=/>fetch params</a> whose
  <a for="fetch params">request</a> is <var>request</var>,