Dramatically increase the performance of Observatory's profile UI

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">
 <link rel="import" href="view_footer.html">
 
 <polymer-element name="sample-buffer-control" extends="observatory-element">
   <template>
@@ skipping 219 matching lines @@
         <th>Method</th>
         <th>Executing</th>
       </tr>
       </thead>
       <tbody id="treeBody">
       </tbody>
     </table>
   </template>
 </polymer-element>
 
+<polymer-element name="cpu-profile-virtual-tree" extends="observatory-element">
+  <template>
+    <link rel="stylesheet" href="css/shared.css">
+    <style>
+    .full {
+      height: 50%;
+      width: 100%;
+    }
+    </style>
+    <div id="tree" class="full"></div>
+  </template>
+</polymer-element>
+
+
 <polymer-element name="cpu-profile-table" extends="observatory-element">
   <template>
     <link rel="stylesheet" href="css/shared.css">
     <nav-bar>
       <top-nav-menu></top-nav-menu>
       <vm-nav-menu vm="{{ isolate.vm }}"></vm-nav-menu>
       <isolate-nav-menu isolate="{{ isolate }}"></isolate-nav-menu>
       <nav-menu link="{{ makeLink('/profiler-table', isolate) }}" anchor="cpu profile (table)" last="{{ true }}"></nav-menu>
       <nav-refresh callback="{{ refresh }}"></nav-refresh>
       <nav-refresh callback="{{ clearCpuProfile }}" label="Clear"></nav-refresh>
@@ skipping 215 matching lines @@
     <style>
       .tableWell {
         background-color: #ECECEC;
         padding: 0.2em;
       }
     </style>
     <sample-buffer-control id="sampleBufferControl"></sample-buffer-control>
     <br>
     <stack-trace-tree-config id="stackTraceTreeConfig"></stack-trace-tree-config>
     <br>
-    <div class="content-centered-big">
-      <div class="tableWell shadow">
-        <cpu-profile-tree id="cpuProfileTree"></cpu-profile-tree>
-      </div>
-    </div>
-    <view-footer></view-footer>
+    <cpu-profile-virtual-tree class="shadow" id="cpuProfileVirtualTree"></cpu-profile-virtual-tree>
   </template>
 </polymer-element>
 
 <script type="application/dart" src="cpu_profile.dart"></script>