feat: add support for long-animation-frame script attribution (#49706)

* feat: add support for `long-animation-frame` script attribution

* docs: document `AlwaysLogLOAFURL`

* chore: add test

* docs: adjust docs as per PR comment

* fix: test failures

* chore: simplify test

* fix: tests on Windows and Linux

docs/api/command-line-switches.md

@@ -370,6 +370,13 @@ Keep in mind that standalone switches can sometimes be split into individual fea
 
 Finally, you'll need to ensure that the version of Chromium in Electron matches the version of the browser you're using to cross-reference the switches.
 
+### Chromium features relevant to Electron apps
+
+* `AlwaysLogLOAFURL`: enables script attribution for
+  [`long-animation-frame`](https://developer.mozilla.org/en-US/docs/Web/API/Performance_API/Long_animation_frame_timing)
+  `PerformanceObserver` events for non-http(s), non-data, non-blob URLs (such as `file:` or custom
+  protocol URLs).
+
 [app]: app.md
 [append-switch]: command-line.md#commandlineappendswitchswitch-value
 [debugging-main-process]: ../tutorial/debugging-main-process.md

patches/chromium/.patches

@@ -145,3 +145,4 @@ expose_gtk_ui_platform_field.patch
 fix_os_crypt_async_cookie_encryption.patch
 patch_osr_control_screen_info.patch
 graphite_handle_out_of_order_recording_errors.patch
+loaf_add_feature_to_enable_sourceurl_for_all_protocols.patch

patches/chromium/loaf_add_feature_to_enable_sourceurl_for_all_protocols.patch

@@ -0,0 +1,52 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Niklas Wenzel <dev@nikwen.de>
+Date: Wed, 4 Feb 2026 06:02:40 -0800
+Subject: LoAF: Add feature to enable sourceURL for all protocols
+
+Backports https://crrev.com/c/7510894 (minus the test changes).
+
+Can be removed when that CL is included via a Chromium roll.
+
+Change-Id: Id5e58a151b13cc0ac054f4ec237b038255d683fd
+Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7510894
+Commit-Queue: Noam Rosenthal <nrosenthal@google.com>
+Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
+Reviewed-by: Noam Rosenthal <nrosenthal@google.com>
+Cr-Commit-Position: refs/heads/main@{#1579397}
+
+diff --git a/third_party/blink/renderer/core/frame/animation_frame_timing_monitor.cc b/third_party/blink/renderer/core/frame/animation_frame_timing_monitor.cc
+index 24e58da8eaa9319e2bb626c69d5ad23de720e108..0ffea9dafe3e3dffcbaf9031082aa88dccb46267 100644
+--- a/third_party/blink/renderer/core/frame/animation_frame_timing_monitor.cc
++++ b/third_party/blink/renderer/core/frame/animation_frame_timing_monitor.cc
+@@ -516,8 +516,15 @@ void AnimationFrameTimingMonitor::Trace(Visitor* visitor) const {
+   visitor->Trace(frame_handling_input_);
+ }
+ 
++BASE_FEATURE(kAlwaysLogLOAFURL, base::FEATURE_DISABLED_BY_DEFAULT);
++
+ namespace {
++
+ bool ShouldAllowScriptURL(const String& url) {
++  if (base::FeatureList::IsEnabled(kAlwaysLogLOAFURL)) {
++    return true;
++  }
++
+   KURL kurl(url);
+   return kurl.ProtocolIsData() || kurl.ProtocolIsInHTTPFamily() ||
+          kurl.ProtocolIs("blob") || kurl.IsEmpty();
+diff --git a/third_party/blink/renderer/core/frame/animation_frame_timing_monitor.h b/third_party/blink/renderer/core/frame/animation_frame_timing_monitor.h
+index f2fe39be2db525d89fcd9787c2ae9285babab26d..c395cf39d404f6c4f6f6e23c9fb8dfe92151a7d2 100644
+--- a/third_party/blink/renderer/core/frame/animation_frame_timing_monitor.h
++++ b/third_party/blink/renderer/core/frame/animation_frame_timing_monitor.h
+@@ -22,6 +22,11 @@ class TimeTicks;
+ 
+ namespace blink {
+ 
++// When enabled, long-animation-frame events will always include the sourceURL,
++// regardless of protocol. This is useful during development when using `file:`
++// URLs or custom protocols defined by embedders.
++CORE_EXPORT BASE_DECLARE_FEATURE(kAlwaysLogLOAFURL);
++
+ class LocalFrame;
+ 
+ // Monitors long-animation-frame timing (LoAF).

spec/chromium-spec.ts

@@ -3280,6 +3280,29 @@ describe('chromium features', () => {
       expect(rgb).to.equal('');
     });
   });
+
+  describe('long-animation-frame', () => {
+    it('should include script attribution on custom protocols if AlwaysLogLOAFURL is enabled', async () => {
+      const rc = await startRemoteControlApp(['--enable-features=AlwaysLogLOAFURL']);
+      const hasAttribution = await rc.remotely(async (fixture: string) => {
+        const { BrowserWindow, protocol, net } = require('electron/main');
+        const { pathToFileURL } = require('node:url');
+
+        protocol.handle('custom', () => net.fetch(pathToFileURL(fixture).toString()));
+
+        // `show: true` is necessary on Windows and Linux due to https://github.com/electron/electron/issues/32001
+        const w = new BrowserWindow({ show: true });
+        await w.loadURL('custom://my-url');
+
+        const hasAttribution = await w.webContents.executeJavaScript('hasAttributionPromise');
+
+        global.setTimeout(() => require('electron').app.quit());
+
+        return hasAttribution;
+      }, path.join(fixturesPath, 'chromium', 'long-animation-frame.html'));
+      expect(hasAttribution).to.be.true();
+    });
+  });
 });
 
 describe('font fallback', () => {

spec/fixtures/chromium/long-animation-frame.html

@@ -0,0 +1,29 @@
+<!doctype html>
+<html>
+  <body>
+    <div id="update"></div>
+    <script>
+      var hasAttributionPromise = new Promise((resolve) => {
+        new PerformanceObserver((list) => {
+          const entries = list.getEntries();
+          const has_attribution =
+            entries.length > 0 &&
+            entries.every(
+              ({ scripts }) =>
+                scripts.length > 0 &&
+                scripts.every(({ sourceURL }) => sourceURL === location.href),
+            );
+          resolve(has_attribution);
+        }).observe({ entryTypes: ["long-animation-frame"] });
+
+        // Produce a long animation frame
+        requestAnimationFrame(() => {
+          const before = performance.now();
+          document.querySelector("#update").innerHTML = "Update";
+          while (performance.now() < before + 60) {}
+          requestAnimationFrame(() => {});
+        });
+      });
+    </script>
+  </body>
+</html>