Merge 025c2d7b8a into bb9ac40252

src/extension-support/extension-manager.js

@@ -4,6 +4,8 @@ const maybeFormatMessage = require('../util/maybe-format-message');
 
 const BlockType = require('./block-type');
 
+let rejectUnofficialExtensions = true;
+
 // These extensions are currently built into the VM repository but should not be loaded at startup.
 // TODO: move these out into a separate repository?
 // TODO: change extension spec so that library info, including extension ID, can be collected through static methods
@@ -154,6 +156,10 @@ class ExtensionManager {
             this._loadedExtensions.set(extensionURL, serviceName);
             return Promise.resolve();
         }
+        
+        if (rejectUnofficialExtensions) {
+            return Promise.reject(new Error('Unofficial extensions not supported here'));
+        }
 
         return new Promise((resolve, reject) => {
             // If we `require` this at the global level it breaks non-webpack targets, including tests