Add candidatepairadded event

This event adds symmetry to the candidate pair lifecycle, so apps
are informed of both candidate pair formation and pruning.

The candidatepairadded event is not strictly necessary for the
pruneproposed event, but makes it easier to use.

index.html

@@ -750,11 +750,25 @@ <h3>
     </ol>
     <pre class="idl">
       partial interface RTCIceTransport {
+        attribute EventHandler oncandidatepairadded;
         attribute EventHandler oncandidatepairpruneproposed;
       };</pre>
     <section>
       <h2>Attributes</h2>
       <dl data-link-for="RTCIceTransport" data-dfn-for="RTCIceTransport" class="attributes">
+        <dt>
+          <dfn>oncandidatepairadded</dfn> of type <span class="idlAttrType">{{EventHandler}}</span>
+        </dt>
+        <dd>
+          <p>
+            The event type of this event handler is {{candidatepairadded}}.
+          </p>
+          <p>
+            When the [= ICE agent =] has formed a candidate pair, the [= user agent =] MUST queue a task to [= fire an
+            event =] named {{candidatepairadded}} using the {{RTCIceCandidatePairEvent}} interface with the
+            {{RTCIceCandidatePairEvent/candidatePair}} attribute set to the formed candidate pair.
+          </p>
+        </dd>
         <dt>
           <dfn>oncandidatepairpruneproposed</dfn> of type <span class="idlAttrType">{{EventHandler}}</span>
         </dt>
@@ -774,7 +788,7 @@ <h2>
         <dfn>RTCIceCandidatePairEvent</dfn>
       </h2>
       <p>
-        The {{RTCIceTransport/candidatepairpruneproposed}} event uses the {{RTCIceCandidatePairEvent}} interface.
+        The {{RTCIceTransport/candidatepairadded}} and {{RTCIceTransport/candidatepairpruneproposed}} events use the {{RTCIceCandidatePairEvent}} interface.
       </p>
       <div>
         <pre class="idl">[Exposed=Window]
@@ -1250,6 +1264,13 @@ <h2>Event summary</h2>
         </tr>
       </thead>
       <tbody>
+        <tr>
+          <th scope=row><dfn data-dfn-for="RTCIceTransport" data-dfn-type=event>candidatepairadded</dfn></th>
+          <td>{{RTCIceCandidatePairEvent}}</td>
+          <td>
+            The [= ICE agent =] has formed a candidate pair and is making it available to the script.
+          </td>
+        </tr>
         <tr>
           <th scope=row><dfn data-dfn-for="RTCIceTransport" data-dfn-type=event>candidatepairpruneproposed</dfn></th>
           <td>{{RTCIceCandidatePairEvent}}</td>