DevTools: Use tooltip for Server Timing metrics

Author: Noj Vek
Bug: 1000373
Change-Id: Ia428114d4666c49b195d903efb79882d481478eb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1788466
Auto-Submit: Paul Irish <[email protected]>
Reviewed-by: Erik Luo <[email protected]>
Commit-Queue: Erik Luo <[email protected]>
Cr-Original-Commit-Position: refs/heads/master@{#694140}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 63927bfa15f15e7c39d1284f0cd45b849ee73218
diff --git a/front_end/network/RequestTimingView.js b/front_end/network/RequestTimingView.js
index 24b3a4a..2623fbf 100644
--- a/front_end/network/RequestTimingView.js
+++ b/front_end/network/RequestTimingView.js
@@ -301,7 +301,9 @@
       const isTotal = serverTiming.metric.toLowerCase() === 'total';
       const tr = tableElement.createChild('tr', isTotal ? 'network-timing-footer' : '');
       const metric = tr.createChild('td', 'network-timing-metric');
-      metric.createTextChild(serverTiming.description || serverTiming.metric);
+      const description = serverTiming.description || serverTiming.metric;
+      metric.createTextChild(description);
+      metric.title = description;
       const row = tr.createChild('td').createChild('div', 'network-timing-row');
 
       if (serverTiming.value === null)