Report some Loaf data in upcoming Chrome

browserscripts/pageinfo/loaf.js

@@ -0,0 +1,36 @@
+(function() {
+    // See https://developer.chrome.com/docs/web-platform/long-animation-frames
+    if (PerformanceObserver.supportedEntryTypes.includes('long-animation-frame')) {
+
+    const MAX_LOAFS_TO_CONSIDER = 10;
+    const relevantLoadEntries = [];
+    const observer = new PerformanceObserver(list => {
+        let longestBlockingLoAFs = [].concat(list.getEntries()).sort(
+          (a, b) => b.blockingDuration - a.blockingDuration
+        ).slice(0, MAX_LOAFS_TO_CONSIDER);
+
+        // re-package
+        for (let entry of longestBlockingLoAFs) {
+            const info = {};
+                info.blockingDuration = entry.blockingDuration;
+                info.duration = entry.duration;
+                info.styleAndLayoutStart = entry.styleAndLayoutStart;
+                info.renderStart = entry.renderStart;
+                info.scripts = [];
+                for (let script of entry.scripts) {
+                    const s = {};
+                    s.forcedStyleAndLayoutDuration = script.forcedStyleAndLayoutDuration;
+                    s.invoker = script.invoker;
+                    s.invokerType = script.invokerType;
+                    s.sourceFunctionName = script.sourceFunctionName;
+                    s.sourceURL = script.sourceURL;
+                    info.scripts.push(s);
+                }
+                relevantLoadEntries.push(info);
+          }
+        return relevantLoadEntries;
+      });
+      observer.observe({ type: 'long-animation-frame', buffered: true });
+    }
+})();
+