Begin to enable extension APIs in Extension Service Worker.

extensions/common/features/feature_util.h

Index: extensions/common/features/feature_util.h
diff --git a/extensions/common/features/feature_util.h b/extensions/common/features/feature_util.h
index f8d60061e6205112be0cfeb7e4dcd33427ea8a35..6c6bc6a9000b411bc6ad221a2e23c224112e047b 100644
--- a/extensions/common/features/feature_util.h
+++ b/extensions/common/features/feature_util.h
@@ -28,4 +28,18 @@
     LOG(FATAL) << message_copy;                                                \
   }
 
+namespace extensions {
+namespace feature_util {
+
+// Returns whether or not extension APIs are allowed in extension service
+// workers.
+// This is currently disallowed as the code to support this is work in progress.
+// Can be overridden in tests.
+bool ExtensionAPIEnabledInExtensionServiceWorkers();
+
+void SetExtensionAPIEnabledInExtensionServiceWorkers(bool enabled);
+
+}  // namespace feature_util
+}  // namespace extensions
+
 #endif  // EXTENSIONS_COMMON_FEATURES_FEATURE_UTIL_H_