Add leakDetectionMetric for tracing

tracing/tracing/model/memory_dump_test_utils.html

Index: tracing/tracing/model/memory_dump_test_utils.html
diff --git a/tracing/tracing/model/memory_dump_test_utils.html b/tracing/tracing/model/memory_dump_test_utils.html
index aa0300e65d4742dd9f3197ca38fc85ee35d6a3fb..8276f5cb055fcb47e0fd5cc7ac409794c03f297c 100644
--- a/tracing/tracing/model/memory_dump_test_utils.html
+++ b/tracing/tracing/model/memory_dump_test_utils.html
@@ -124,6 +124,8 @@ tr.exportTo('tr.model', function() {
         dump.addNumeric(numericName, castToScalar(value));
       }
     }
+    const children = getOption(opt_options, 'children');
+    if (children) dump.children = children;
     return dump;
   };