Disables kAllowURNsInIframes feature.

Chromium change:

https://source.chromium.org/chromium/chromium/src/+/8e7fdeb8e1e47142b9a6ca42e1f01fb74d493171

commit 8e7fdeb8e1e47142b9a6ca42e1f01fb74d493171
Author: Russ Hamilton <behamilton@google.com>
Date:   Sun Dec 5 20:05:31 2021 +0000

    Add and implement AllowURNsInIframes feature

    This feature, when enabled, allows frames other than fenced frames to
    translate urn:uuid based on a fenced frame mapping

    Bug: 1271994

app/brave_main_delegate_browsertest.cc

@@ -91,6 +91,7 @@ IN_PROC_BROWSER_TEST_F(BraveMainDelegateBrowserTest, DisabledFeatures) {
     &autofill::features::kAutofillEnableAccountWalletStorage,
     &autofill::features::kAutofillServerCommunication,
     &blink::features::kAdInterestGroupAPI,
+    &blink::features::kAllowURNsInIframes,
     &blink::features::kComputePressure,
     &blink::features::kConversionMeasurement,
     &blink::features::kCssSelectorFragmentAnchor,

chromium_src/third_party/blink/common/features.cc

@@ -17,6 +17,7 @@ OVERRIDE_FEATURE_DEFAULT_STATES({{
     {kReducedReferrerGranularity, base::FEATURE_ENABLED_BY_DEFAULT},
 
     {kAdInterestGroupAPI, base::FEATURE_DISABLED_BY_DEFAULT},
+    {kAllowURNsInIframes, base::FEATURE_DISABLED_BY_DEFAULT},
     {kComputePressure, base::FEATURE_DISABLED_BY_DEFAULT},
     {kConversionMeasurement, base::FEATURE_DISABLED_BY_DEFAULT},
     {kCssSelectorFragmentAnchor, base::FEATURE_DISABLED_BY_DEFAULT},