Display Histograms in value-set-table-cells.

tracing/tracing/value/ui/diagnostic_map_table.html

Index: tracing/tracing/value/ui/diagnostic_map_table.html
diff --git a/tracing/tracing/value/ui/diagnostic_map_table.html b/tracing/tracing/value/ui/diagnostic_map_table.html
index dc8cdf7574294d94e948dbf9124f260b1084c4d1..508558a6010154e1d5e4870117e561038478c70f 100644
--- a/tracing/tracing/value/ui/diagnostic_map_table.html
+++ b/tracing/tracing/value/ui/diagnostic_map_table.html
@@ -56,7 +56,11 @@ found in the LICENSE file.
         return {
           title: title,
           value: function(map) {
-            return tr.v.ui.createDiagnosticSpan(map.get(title));
+            var diagnostic = map.get(title);
+            if (!diagnostic)
+              return '';
+
+            return tr.v.ui.createDiagnosticSpan(diagnostic);
           }
         };
       }