Add source "cpu-same-origin"

Adding "cpu-same-origin" as source.

index.html

@@ -162,7 +162,7 @@ <h3>Supported sources</h3>
       Future levels of this specification MAY introduce additional [=source types=].
     </p>
     <pre class="idl">
-      enum PressureSource { "thermals", "cpu" };
+      enum PressureSource { "thermals", "cpu", "cpu-same-origin" };
     </pre>
     <p>
       The <dfn>PressureSource</dfn> enum represents the [=supported source types=]:
@@ -176,6 +176,11 @@ <h3>Supported sources</h3>
           {{PressureSource/"cpu"}} represents the average pressure of the central [=processing unit=]
           across all its cores.
         </li>
+        <li>
+          {{PressureSource/"cpu-same-origin"}} represents the average pressure of the central [=processing unit=]
+          across all its cores for all contexts the site is using (this includes the main thread for the window
+          and same origin iframes, and workers).
+        </li>
       </ul>
     </p>
     <aside class="note">