Expose a minimized Content-Type to Resource Timing

This defines the content type field as a minimized version of the response's parsed Content-Type header, to give web developers enough information to distinguish responses, but not enough to make it an additional communication channel.

This feature will be used by Resource Timing as per w3c/resource-timing#341.

Co-authored-by: Anne van Kesteren <[email protected]>

Author: abinpaul1

fetch.bs

@@ -362,11 +362,13 @@ information needed by <cite>Resource Timing</cite> and <cite>Navigation Timing</
 following <a for=struct>items</a>: [[RESOURCE-TIMING]] [[NAVIGATION-TIMING]]
 
 <dl>
- <dt><dfn export for="response body info" id="fetch-timing-info-encoded-body-size">encoded
- size</dfn> (default 0)
- <dt><dfn export for="response body info" id="fetch-timing-info-decoded-body-size">decoded
- size</dfn> (default 0)
+ <dt><dfn export for="response body info" id="fetch-timing-info-encoded-body-size">encoded size</dfn>
+ (default 0)
+ <dt><dfn export for="response body info" id="fetch-timing-info-decoded-body-size">decoded size</dfn>
+ (default 0)
  <dd>A number.
+ <dt><dfn export for="response body info">content type</dfn> (default the empty string)
+ <dd>An <a for=/>ASCII string</a>.
 </dl>
 
 <div algorithm>
@@ -4755,6 +4757,21 @@ steps:
      <var>response</var>'s <a for=response>has-cross-origin-redirects</a> is true; otherwise
      <var>response</var>'s <a for=response>status</a>.
 
+     <li>
+      <p>If <var>fetchParams</var>'s <a for="fetch params">request</a>'s <a for=request>mode</a> is
+      not "<code>navigate</code>" or <var>response</var>'s
+      <a for=response>has-cross-origin-redirects</a> is false:
+
+      <ol>
+       <li><p>Let <var>mimeType</var> be the result of
+       <a for="header list">extracting a MIME type</a> from <var>response</var>'s
+       <a for=response>header list</a>.
+
+       <li><p>If <var>mimeType</var> is non-null, then set <var>bodyInfo</var>'s
+       <a for="response body info">content type</a> to the result of
+       <a>minimizing a supported MIME type</a> given <var>mimeType</var>.
+      </ol>
+
      <li><p>If <var>fetchParams</var>'s <a for="fetch params">request</a>'s
      <a for=request>initiator type</a> is non-null, then <a for=/>mark resource timing</a> given
      <var>timingInfo</var>, <var>fetchParams</var>'s <a for="fetch params">request</a>'s