Fix memory leak in CPU Profile page

runtime/observatory/lib/src/elements/cpu_profile.html

 <link rel="import" href="../../../../packages/polymer/polymer.html">
 <link rel="import" href="code_ref.html">
 <link rel="import" href="function_ref.html">
 <link rel="import" href="nav_bar.html">
 <link rel="import" href="observatory_element.html">
 <link rel="import" href="sliding_checkbox.html">
 
 <polymer-element name="cpu-profile" extends="observatory-element">
   <template>
     <link rel="stylesheet" href="css/shared.css">
@@ skipping 139 matching lines @@
                 <option value="VMUser">VM &gt; User</option>
                 <option value="VMOnly">VM</option>
                 <option value="None">None</option>
               </select>
             </div>
           </div>
           <div class="memberItem">
             <div class="memberName">Call Tree Direction</div>
             <div class="memberValue">
               <select value="{{directionSelector}}">
-                <!-- Experimental: <option value="Down">Top down</option> -->
+                <!--- Experimental <option value="Down">Top down</option> --->
                 <option value="Up">Bottom up</option>
               </select>
             </div>
           </div>
         </div>
       </template>
       <template if="{{ state == 'Loaded' && directionSelector == 'Down' }}">
         <br>
         <div class="statusBox shadow">
           <div>Tree is rooted at main.</div>
           <br>
           <div>Child nodes are callees.</div>
           <br>
           <div class="notice">To get the most out of this mode you may need to launch Dart with a higher --profile-depth flag value.</div>
-          <div class="notice">Try 16, 32, ... up to 256 until each sample captures the entire call stack.</div>
+          <div class="notice">Try 16, 32, ... up to 256 until [Truncated] approaches zero.</div>
           <div class="red">NOTE: Higher values will impact performance</div>
         </div>
       </template>
       <template if="{{ state == 'Loaded' && directionSelector == 'Up' }}">
         <br>
         <div class="statusBox shadow">
           <div>Tree is rooted at executing function / code.</div>
           <br>
           <div>Child nodes are callers.</div>
         </div>
       </template>
       <br><br>
       <div class="tableWell shadow">
         <table class="table">
           <thead id="treeHeader">
           <tr>
             <th>Method</th>
             <th>Self</th>
           </tr>
           </thead>
           <tbody id="treeBody">
           </tbody>
         </table>
       </div>
     </div>
   </template>
 </polymer-element>
 
 <script type="application/dart" src="cpu_profile.dart"></script>