Switch tracing to new flexbox.

tracing/tracing_examples/chrome_inspect_test_shell.html

Index: tracing/tracing_examples/chrome_inspect_test_shell.html
diff --git a/tracing/tracing_examples/chrome_inspect_test_shell.html b/tracing/tracing_examples/chrome_inspect_test_shell.html
index dc939dfc9bbc631f23e5110639a8454977cd16cb..e26bad7b8942a8aec6974af00eb408d367512625 100644
--- a/tracing/tracing_examples/chrome_inspect_test_shell.html
+++ b/tracing/tracing_examples/chrome_inspect_test_shell.html
@@ -18,12 +18,12 @@ found in the LICENSE file.
     padding: 0;
     width: 100%;
     height: 100%;
-    display: -webkit-flex;
-    -webkit-flex-direction: column;
+    display: flex;
+    flex-direction: column;
   }
 
   body > x-profiling-view {
-    -webkit-flex: 1 1 auto;
+    flex: 1 1 auto;
     overflow: hidden;
     position: absolute;
     top: 0px;
@@ -38,7 +38,7 @@ found in the LICENSE file.
   <script>
   'use strict';
 
-  var profilingViewEl;
+  let profilingViewEl;
 
   function onLoad() {
     if (window.DevToolsHost === undefined) {
@@ -53,7 +53,7 @@ found in the LICENSE file.
       return;
     }
 
-    var tracingControllerClient = new tr.ui.e.about_tracing.InspectorTracingControllerClient(); // @suppress longLineCheck
+    const tracingControllerClient = new tr.ui.e.about_tracing.InspectorTracingControllerClient(); // @suppress longLineCheck
     profilingViewEl = new tr.ui.e.about_tracing.ProfilingView(tracingControllerClient); // @suppress longLineCheck
     document.body.appendChild(profilingViewEl);
   }