Getting connectionList now always returns the same object

This update should address last Pull Request comments, as well as #281.

Note I ended up introducing two new idioms to talk about the Promise and
PresentationConnectionList singletons, as I believe it improves the readability
of algorithms, and makes the list of objects that user agents need to maintain
explicit.

However, as usual, finding names for things is hard. I came up with
"presentation controllers monitor" and "presentation controllers promise".
It may be possible to find better names. For instance, instead of "monitor", we
could use "manager", "holder", "wrapper", "container".

index.html

@@ -728,6 +728,22 @@ <h3>
           connections</a> in this set share the same <a>presentation URL</a>
           and <a>presentation identifier</a>.
         </p>
+        <p>
+          In a <a>receiving browsing context</a>, the <dfn>presentation
+          controllers monitor</dfn>, initially set to <code>null</code>,
+          exposes the current <a>set of presentation controllers</a> to the
+          receiving application. The <a>presentation controllers monitor</a> is
+          represented by a <a>PresentationConnectionList</a>.
+        </p>
+        <p>
+          In a <a>receiving browsing context</a>, the <dfn>presentation
+          controllers promise</dfn>, which is initially set to
+          <code>null</code>, exposes the <a>presentation controllers
+          monitor</a> once the initial <a>presentation connection</a> is
+          established. The <a>presentation controllers promise</a> is
+          represented by a <a>Promise</a> that holds the <a>presentation
+          controllers monitor</a>.
+        </p>
       </section>
       <section>
         <h3>
@@ -1524,10 +1540,9 @@ <h4>
             A <a>receiving user agent</a> <a>fires</a> a <a>trusted event</a>
             named <a for="PresentationConnectionList">connectionavailable</a>
             on a <a>PresentationReceiver</a> when an incoming connection is
-            created. It is fired at the <a>PresentationConnectionList</a>
-            instance associated with the <a>PresentationReceiver</a> instance,
-            using the <a>PresentationConnectionAvailableEvent</a> interface,
-            with the <a for=
+            created. It is fired at the <a>presentation controllers
+            monitor</a>, using the <a>PresentationConnectionAvailableEvent</a>
+            interface, with the <a for=
             "PresentationConnectionAvailableEvent">connection</a> attribute set
             to the <a><code>PresentationConnection</code></a> object that was
             created. The event is fired for all connections that are created
@@ -2282,34 +2297,35 @@ <h3>
           be implemented in a <a>receiving browsing context</a> provided by a
           <a>receiving user agent</a>.
         </p>
-        <p>
-          When the <a>PresentationReceiver</a> object is created, a
-          <a>PresentationConnectionList</a> object is also created and
-          associated with that <a>PresentationReceiver</a> object.
-        </p>
         <p>
           On getting, the <dfn for="PresentationReceiver">connectionList</dfn>
           attribute MUST return the result of running the following steps:
         </p>
         <ol>
-          <li>If there is already an unsettled <a>Promise</a> <var>P</var> from
-          a previous call to get the <a for=
-          "PresentationReceiver">connectionList</a> attribute for the same <a>
-            PresentationReceiver</a> object, return <var>P</var> and abort all
-            remaining steps.
+          <li>If the <a>presentation controllers promise</a> is not
+          <code>null</code>, return the <a>presentation controllers promise</a>
+          and abort all remaining steps.
           </li>
-          <li>Let <var>P</var> be a new <a>Promise</a>.
+          <li>Otherwise, let the <a>presentation controllers promise</a> be a
+          new <a>Promise</a>.
           </li>
-          <li>Return <var>P</var>, but continue running these steps <a>in
-          parallel</a>.
+          <li>Return the <a>presentation controllers promise</a>, but continue
+          running these steps <a>in parallel</a>.
           </li>
           <li>If the <a>set of presentation controllers</a> contains at least
-          one <a>presentation connection</a>, <a>resolve</a> <var>P</var> with
-          the <a>PresentationConnectionList</a> object associated with the <a>
-            PresentationReceiver</a> object.
+          one <a>presentation connection</a>, then run the following steps:
+            <ol>
+              <li>Let the <a>presentation controllers monitor</a> be a new <a>
+                PresentationConnectionList</a>.
+              </li>
+              <li>
+                <a>Resolve</a> the <a>presentation controllers promise</a> with
+                the <a>presentation controllers monitor</a>.
+              </li>
+            </ol>
           </li>
-          <li>Otherwise, <var>P</var> remains unsettled and associated with the
-          <a>PresentationReceiver</a> object.
+          <li>Otherwise, the <a>presentation controllers promise</a> remains
+          unsettled.
           </li>
         </ol>
         <section>
@@ -2423,24 +2439,31 @@ <h4>
             </li>
             <li>Add <var>S</var> to the <a>set of presentation controllers</a>.
             </li>
-            <li>If there is an unsettled <a>Promise</a> <var>P</var> from a
-            previous call to get the <a for=
-            "PresentationReceiver">connectionList</a> attribute for the same
-            <a>PresentationReceiver</a> object, <a>resolve</a> <var>P</var>
-            with the <a>PresentationConnectionList</a> object associated with
-            the <a>PresentationReceiver</a> object and abort all remaining
-            steps.
+            <li>If the <a>presentation controllers promise</a> is
+            <code>null</code>, then abort all remaining steps.
             </li>
-            <li>
-              <a>Queue a task</a> to <a>fire</a> a <a>trusted event</a> with
-              the name <a for=
-              "PresentationConnectionList">connectionavailable</a>, that uses
-              the <a>PresentationConnectionAvailableEvent</a> interface, with
-              the <a for="PresentationConnectionAvailableEvent">connection</a>
-              attribute initialized to <var>S</var>, at the
-              <a>PresentationConnectionList</a> object associated with the
-              <a>PresentationReceiver</a> object. The event must not bubble,
-              must not be cancelable, and has no default action.
+            <li>Otherwise, if the <a>presentation controllers promise</a> is
+            unsettled, then run the following steps:
+              <ol>
+                <li>Let the <a>presentation controllers monitor</a> be a new
+                <a>PresentationConnectionList</a>.
+                </li>
+                <li>
+                  <a>Resolve</a> the <a>presentation controllers promise</a>
+                  with the <a>presentation controllers monitor</a>.
+                </li>
+                <li>Abort all remaining steps.
+                </li>
+              </ol>
+            </li>
+            <li>Otherwise, <a>queue a task</a> to <a>fire</a> a <a>trusted
+            event</a> with the name <a for=
+            "PresentationConnectionList">connectionavailable</a>, that uses the
+            <a>PresentationConnectionAvailableEvent</a> interface, with the
+            <a for="PresentationConnectionAvailableEvent">connection</a>
+            attribute initialized to <var>S</var>, at the <a>presentation
+            controllers monitor</a>. The event must not bubble, must not be
+            cancelable, and has no default action.
             </li>
           </ol>
           <p>