Integrate with Fetch Metadata Request Headers

Tests: fetch/metadata.

Closes #885.

fetch.bs

@@ -123,6 +123,7 @@ everything that involves, including:
  <li>Redirects
  <li>Cross-origin semantics
  <li>CSP [[!CSP]]
+ <li>Fetch Metadata [[!FETCH-METADATA]]
  <li>Service workers [[!SW]]
  <li>Mixed Content [[!MIX]]
  <li>`<code>Referer</code>` [[!REFERRER]]
@@ -1671,13 +1672,18 @@ a given context. [[!CSP]]
 <dfn export for=request id=concept-request-reload-navigation-flag>reload-navigation flag</dfn>.
 Unless stated otherwise, it is unset.
 
-<p class="note no-backref">This flag is for exclusive use by HTML's navigate algorithm. [[!HTML]]
+<p class=note>This flag is for exclusive use by HTML's navigate algorithm. [[!HTML]]
 
 <p>A <a for=/>request</a> has an associated
 <dfn export for=request id=concept-request-history-navigation-flag>history-navigation flag</dfn>.
 Unless stated otherwise, it is unset.
 
-<p class="note no-backref">This flag is for exclusive use by HTML's navigate algorithm. [[!HTML]]
+<p class=note>This flag is for exclusive use by HTML's navigate algorithm. [[!HTML]]
+
+<p>A <a for=/>request</a> has an associated boolean <dfn export for=request>user-activation</dfn>.
+Unless stated otherwise, it is false.
+
+<p class=note>This is for exclusive use by HTML's navigate algorithm. [[!HTML]]
 
 <hr>
 
@@ -4276,6 +4282,9 @@ steps. They return a <a for=/>response</a>.
 
    <li><p><a>Append a request `<code>Origin</code>` header</a> for <var>httpRequest</var>.
 
+   <li><p><a abstract-op lt="append the Fetch metadata headers for a request">Append the Fetch metadata headers for <var>httpRequest</var></a>.
+   [[!FETCH-METADATA]]
+
    <li><p>If <var>httpRequest</var>'s <a for=request>header list</a>
    <a for="header list">does not contain</a> `<code>User-Agent</code>`, then user agents should
    <a for="header list">append</a>