anchor.diff:            let scriptTag = document.createElement("script");
             scriptTag.src = entrypointUrl;
             scriptTag.type = "application/javascript";
  -          this._didCreateEngineInitializerResolve = resolve; // Cache the resolve, so it can be called from Flutter.
  +          // Cache the resolve, so it can be called from Flutter.
  +          // Note: Flutter hot restart doesn't re-create this promise, so this
  +          // can only be called once. Instead, we need to model this as a stream
  +          // of `engineCreated` events coming from Flutter that are handled by JS.
  +          this._didCreateEngineInitializerResolve = resolve;
             scriptTag.addEventListener("error", reject);
             document.body.append(scriptTag);
           });
  
positive.code: (function() {
    "use strict";
    class FlutterLoader {
      // TODO: Move the below methods to "#private" once supported by all the browsers
      // we support. In the meantime, we use the "revealing module" pattern.
  
      // Watchdog to prevent injecting the main entrypoint multiple times.
      _scriptLoaded = null;
  
      // Resolver for the pending promise returned by loadEntrypoint.
      _didCreateEngineInitializerResolve = null;
  
      /**
       * Initializes the main.dart.js with/without serviceWorker.
  
negative.code:     }
  
      /**
       * Resolves the promise created by loadEntrypoint.
       * Called by Flutter through the public `didCreateEngineInitializer` method,
       * which is bound to the correct instance of the FlutterLoader on the page.
       * @param {*} engineInitializer
       */
      _didCreateEngineInitializer(engineInitializer) {
        if (typeof this._didCreateEngineInitializerResolve != "function") {
          console.warn("Do not call didCreateEngineInitializer by hand. Start with loadEntrypoint instead.");
        }
        this._didCreateEngineInitializerResolve(engineInitializer);
        // Remove the public method after it's done, so Flutter Web can hot restart.
        delete this.didCreateEngineInitializer;
      }
  
      _loadEntrypoint(entrypointUrl) {
        if (!this._scriptLoaded) {
  