Move enable extensions define to a build flag.

components/policy/core/common/schema_registry_unittest.cc

Index: components/policy/core/common/schema_registry_unittest.cc
diff --git a/components/policy/core/common/schema_registry_unittest.cc b/components/policy/core/common/schema_registry_unittest.cc
index 08134d2f7d9b250d0f3e30f2dba6062afa647992..b9fdbf117c4e62f9564c9335294daa1c3c596688 100644
--- a/components/policy/core/common/schema_registry_unittest.cc
+++ b/components/policy/core/common/schema_registry_unittest.cc
@@ -8,6 +8,7 @@
 
 #include "components/policy/core/common/policy_namespace.h"
 #include "components/policy/core/common/schema.h"
+#include "extensions/features/features.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -114,7 +115,7 @@ TEST(SchemaRegistryTest, IsReady) {
   registry.AddObserver(&observer);
 
   EXPECT_FALSE(registry.IsReady());
-#if defined(ENABLE_EXTENSIONS)
+#if BUILDFLAG(ENABLE_EXTENSIONS)
   EXPECT_CALL(observer, OnSchemaRegistryReady()).Times(0);
   registry.SetExtensionsDomainsReady();
   Mock::VerifyAndClearExpectations(&observer);