Re-enable ReportingObserver and make noop

browser/test/disabled_features/reporting_observer_browsertest.cc

@@ -32,11 +32,11 @@ class ReportingObserverTest : public InProcessBrowserTest {
   }
 };
 
-IN_PROC_BROWSER_TEST_F(ReportingObserverTest, IsDisabled) {
+IN_PROC_BROWSER_TEST_F(ReportingObserverTest, IsNoop) {
   GURL url = embedded_test_server()->GetURL(kReportingObserver);
   ASSERT_TRUE(ui_test_utils::NavigateToURL(browser(), url));
   content::WebContents* contents =
       browser()->tab_strip_model()->GetActiveWebContents();
 
-  EXPECT_EQ(true, EvalJs(contents, "isReportingObserverDisabled();"));
+  EXPECT_EQ(true, EvalJs(contents, "isReportingObserverNoop();"));
 }

chromium_src/third_party/blink/renderer/core/frame/reporting_observer.cc

@@ -0,0 +1,21 @@
+/* Copyright (c) 2024 The Brave Authors. All rights reserved.
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+#include "third_party/blink/renderer/core/frame/reporting_observer.h"
+
+#define QueueReport QueueReport_Unused
+#include "src/third_party/blink/renderer/core/frame/reporting_observer.cc"
+#undef QueueReport
+
+namespace blink {
+
+void ReportingObserver::QueueReport(Report* report) {
+  // Don't add reports. We previously used to disable ReportingObserver in
+  // Brave, but for webcompat reasons, we now just no-op it. This makes
+  // takeRecords() always return an empty list.
+  return;
+}
+
+}  // namespace blink

chromium_src/third_party/blink/renderer/core/frame/reporting_observer.h

@@ -0,0 +1,17 @@
+/* Copyright (c) 2024 The Brave Authors. All rights reserved.
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+#ifndef BRAVE_CHROMIUM_SRC_THIRD_PARTY_BLINK_RENDERER_CORE_FRAME_REPORTING_OBSERVER_H_
+#define BRAVE_CHROMIUM_SRC_THIRD_PARTY_BLINK_RENDERER_CORE_FRAME_REPORTING_OBSERVER_H_
+
+#define QueueReport                   \
+  QueueReport_Unused(Report* report); \
+  void QueueReport
+
+#include "src/third_party/blink/renderer/core/frame/reporting_observer.h"  // IWYU pragma: export
+
+#undef QueueReport
+
+#endif  // BRAVE_CHROMIUM_SRC_THIRD_PARTY_BLINK_RENDERER_CORE_FRAME_REPORTING_OBSERVER_H_

test/data/reporting_observer.html

@@ -1,11 +1,21 @@
 <script>
-  function isReportingObserverDisabled() {
+  function isReportingObserverNoop() {
     try {
-      new ReportingObserver(function(reports, observer) {
-      	return false;
-	  }, {});
-    } catch (err) {
-      return true;
+      const observer = new ReportingObserver(() => {},
+        { types: ['deprecation'], buffered: true }
+      );
+      observer.observe();
+      const xhr = new XMLHttpRequest();
+      // false makes it synchronous, which is deprecated.
+      xhr.open('GET', '/', false);
+      xhr.send(null);
+      const reports = observer.takeRecords();
+      console.log("Reports:", reports);
+      // Even though we made a synchronous request, we should not have any reports.
+      return reports.length === 0;
+    } catch (error) {
+      console.error("Error occurred:", error);
+      return false;
     }
   }
 </script>