Add "validated" to response's cache state

For Resource Timing's transferSize. Corresponding RT PR: w3c/resource-timing#272.

Tests: https://chromium-review.googlesource.com/c/chromium/src/+/2878693.

Author: yoavweiss

fetch.bs

@@ -1938,8 +1938,9 @@ message as HTTP/2 does not support them.
 <a for=/>response</a>'s <a for=response>body</a> are always null.
 
 <p>A <a for=/>response</a> has an associated
-<dfn export for=response id=concept-response-cache-state>cache state</dfn> (the empty string or
-"<code>local</code>"). Unlesss stated otherwise, it is the empty string.
+<dfn export for=response id=concept-response-cache-state>cache state</dfn> (the empty string,
+"<code>local</code>", or "<code>validated</code>"). Unlesss stated otherwise, it is the empty
+string.
 
 <p class=note>This is intended for usage by <cite>Service Workers</cite> and
 <cite>Resource Timing</cite>.  [[SW]] [[RESOURCE-TIMING]]
@@ -4895,6 +4896,8 @@ steps. They return a <a for=/>response</a>.
 
      <li><p>Set <var>response</var> to <var>storedResponse</var>.
 
+     <li><p>Set <var>response</var>'s <a for=response>cache state</a> to "<code>validated</code>".
+
      <li><p><a for=/>Update timing info from stored response</a> given <var>fetchParams</var>'s
      <a for="fetch params">timing info</a> and <var>response</var>.
     </ol>