Tweak test annotations chapter 7.

Fixes #2464

@dontcallmedom: The test annotations to section 7.4 (RTCDTMFToneChangeEvent)
do not work. Can you take a look?

webrtc.html

@@ -10177,12 +10177,12 @@ <h2>Attributes</h2>
           "attributes">
             <dt><dfn>dtmf</dfn> of type <span class=
             "idlAttrType">{{RTCDTMFSender}}</span>, readonly, nullable</dt>
-            <dd>
+            <dd class="test-needed">
               <p>On getting, the {{dtmf}} attribute returns the value
-              of the <a>[[\Dtmf]]</a>internal slot, which represents a
+              of the <a>[[\Dtmf]]</a> internal slot, which represents a
               {{RTCDTMFSender}} which can be used to send DTMF, or
-              <code>null</code> if unset. The <a>[[\Dtmf]]</a>internal slot is set
-              when the kind of an {{RTCRtpSender}}'s
+              <code>null</code> if unset. The <a>[[\Dtmf]]</a> internal slot
+              is set when the kind of an {{RTCRtpSender}}'s
               <a>[[\SenderTrack]]</a> is <code>"audio"</code>.</p>
             </dd>
           </dl>
@@ -10408,10 +10408,11 @@ <h2>Constructors</h2>
           <h2>Attributes</h2>
           <dl data-link-for="RTCDTMFToneChangeEvent" data-dfn-for=
           "RTCDTMFToneChangeEvent" class="attributes">
-            <dt><dfn data-idl>tone</dfn> of type <span class=
-            "idlAttrType">DOMString</span>, readonly</dt>
+            <dt class="test-needed">
+              <dfn data-idl>tone</dfn> of type
+              <span class="idlAttrType">DOMString</span>, readonly</dt>
             <dd>
-              <p>The {{tone}} attribute contains the
+              <p class="test-needed">The {{tone}} attribute contains the
               character for the tone (including <code>","</code>) that has just
               begun playout (see {{RTCDTMFSender/insertDTMF}} ). If
               the value is the empty string, it indicates that the
@@ -10435,7 +10436,7 @@ <h2>Dictionary <dfn>RTCDTMFToneChangeEventInit</dfn>
             "idlMemberType">DOMString</span>, defaulting to
               <code>""</code></dt>
             <dd>
-              <p>The {{tone}} attribute contains the
+              <p class="test-needed">The {{tone}} attribute contains the
               character for the tone (including <code>","</code>) that has just
               begun playout (see {{RTCDTMFSender/insertDTMF}} ). If
               the value is the empty string, it indicates that the