MD Downloads: add first meaningful paint metrics to UMA

chrome/browser/resources/md_downloads/downloads.js

Index: chrome/browser/resources/md_downloads/downloads.js
diff --git a/chrome/browser/resources/md_downloads/downloads.js b/chrome/browser/resources/md_downloads/downloads.js
index bfed6d1ce0f2aae480a22c85be601b29355160b4..9f934af5bc9228cd9bd2bb048a202047834c4eec 100644
--- a/chrome/browser/resources/md_downloads/downloads.js
+++ b/chrome/browser/resources/md_downloads/downloads.js
@@ -3,6 +3,13 @@
 // found in the LICENSE file.
 
 window.addEventListener('load', function() {
-  downloads.Manager.onLoad();
-  document.fonts.load('bold 12px Roboto');
+  downloads.Manager.onLoad().then(function() {
+    requestIdleCallback(function() {
+      chrome.send('metricsHandler:recordTime', [
+        'Download.ResultsRenderedTime',
+        window.performance.now()
+      ]);
+      document.fonts.load('bold 12px Roboto');
+    });
+  });
 });