Add a revalidation cache state and adapt transferSize to it (#272)

* Rebase

* validated

* merged back gh-pages

* Merged back changes

index.html

@@ -448,7 +448,7 @@ <h3>
         <p>
           A <a>PerformanceResourceTiming</a> has an associated DOMString
           <a data-dfn-for="PerformanceResourceTiming"><dfn>cache mode</dfn></a>
-          (the empty string or "<code>local</code>").
+          (the empty string, "<code>local</code>", or "<code>validated</code>").
         </p>
         <p>
           A <a>PerformanceResourceTiming</a> has an associated [=fetch timing
@@ -640,6 +640,8 @@ <h3>
               mode</a> is "<code>local</code>", then return 0.
             </p>
           </li>
+          <li><p>If <a>this</a>'s <a data-for="PerformanceResourceTiming">cache mode</a> is
+"<code>validated</code>", then return 300.
           <li>
             <p>
               Return <a>this</a>'s <a data-for=