Limit base-class initialization checks to development and TESTING modes

We have a number of base-classes that are only intended to be extended, but never to be used directly. To help enforce this during development these base-class constructors will check for direct usage, however that code is obviously not needed in the actual builds.

*Note:* This patch reduces the size of the `gulp mozcentral` output by `~2.7` kilo-bytes, which isn't a lot but still cannot hurt.

web/app_options.js

@@ -583,7 +583,9 @@ class AppOptions {
   }
 
   constructor() {
-    throw new Error("Cannot initialize AppOptions.");
+    if (typeof PDFJSDev === "undefined" || PDFJSDev.test("TESTING")) {
+      throw new Error("Cannot initialize AppOptions.");
+    }
   }
 
   static get(name) {