Add an ONC property for proactive key caching.

components/onc/docs/onc_spec.html

Index: components/onc/docs/onc_spec.html
diff --git a/components/onc/docs/onc_spec.html b/components/onc/docs/onc_spec.html
index 5f001fcf643ec02676f9d79a6762e5457d70cecc..fb226339969fd48b467752877448d20adc31b47a 100644
--- a/components/onc/docs/onc_spec.html
+++ b/components/onc/docs/onc_spec.html
@@ -2038,6 +2038,16 @@
       is <span class="value">false</span>, and no <span class="field">ServerCARef</span> is set, the certificate
       must be a self signed certificate, and no CA signature is required.
     </dd>
+
+    <dt class="field">UseProactiveKeyCaching</dt>
+    <dd>
+      <span class="field_meta">
+        (optional, defaults to <span class="value">false</span>)
+        <span class="type">boolean</span>
+      </span>
+      Indicates whether Proactive Key Caching (also known as Opportunistic
+      Key Caching) should be used on a per-service basis.
+    </dd>
   </dl>
 
   <p class="rule">