How to use the @angular-devkit/build-webpack.WebpackBuilder function in @angular-devkit/build-webpack

run(builderConfig) {
        const architect = this.context.architect;
        const options = builderConfig.options;
        const root = this.context.workspace.root;
        const projectRoot = core_1.resolve(root, builderConfig.root);
        const [project, targetName, configuration] = options.browserTarget.split(':');
        // Override browser build watch setting.
        const overrides = { watch: false };
        const browserTargetSpec = { project, target: targetName, configuration, overrides };
        const browserBuilderConfig = architect.getBuilderConfiguration(browserTargetSpec);
        const webpackBuilder = new build_webpack_1.WebpackBuilder(this.context);
        const loggingCb = (stats, config, logger) => {
            const json = stats.toJson();
            if (stats.hasWarnings()) {
                this.context.logger.warn(stats_1.statsWarningsToString(json, config.stats));
            }
            if (stats.hasErrors()) {
                this.context.logger.error(stats_1.statsErrorsToString(json, config.stats));
            }
        };
        return architect.getBuilderDescription(browserBuilderConfig).pipe(operators_1.concatMap(browserDescription => architect.validateBuilderOptions(browserBuilderConfig, browserDescription)), operators_1.map(browserBuilderConfig => browserBuilderConfig.options), operators_1.concatMap((validatedBrowserOptions) => {
            const browserOptions = validatedBrowserOptions;
            // We need to determine the outFile name so that AngularCompiler can retrieve it.
            let outFile = options.outFile || getI18nOutfile(options.i18nFormat);
            if (options.outputPath) {
                // AngularCompilerPlugin doesn't support genDir so we have to adjust outFile instead.
                outFile = path.join(options.outputPath, outFile);

run(builderConfig: BuilderConfiguration): Observable {
    console.log('Hi');
    const options = builderConfig.options;
    const root = this.context.workspace.root;
    const projectRoot = resolve(root, builderConfig.root);
    const host = new virtualFs.AliasHost(this.context.host as virtualFs.Host);
    const webpackBuilder = new WebpackBuilder({ ...this.context, host });

    return of(null).pipe(
      concatMap(() => options.deleteOutputPath
        ? this._deleteOutputDir(root, normalize(options.outputPath), this.context.host)
        : of(null)),
      concatMap(() => addFileReplacements(root, host, options.fileReplacements)),
      concatMap(() => normalizeAssetPatterns(
        options.assets, host, root, projectRoot, builderConfig.sourceRoot)),
      // Replace the assets in options with the normalized version.
      tap((assetPatternObjects => options.assets = assetPatternObjects)),
      concatMap(() => {
        // Ensure Build Optimizer is only used with AOT.
        if (options.buildOptimizer && !options.aot) {
          throw new Error('The `--build-optimizer` option cannot be used without `--aot`.');
        }

run(builderConfig) {
        const architect = this.context.architect;
        const options = builderConfig.options;
        const root = this.context.workspace.root;
        const projectRoot = core_1.resolve(root, builderConfig.root);
        const [project, targetName, configuration] = options.browserTarget.split(':');
        // Override browser build watch setting.
        const overrides = { watch: false };
        const browserTargetSpec = { project, target: targetName, configuration, overrides };
        const browserBuilderConfig = architect.getBuilderConfiguration(browserTargetSpec);
        const webpackBuilder = new build_webpack_1.WebpackBuilder(this.context);
        const loggingCb = (stats, config, logger) => {
            const json = stats.toJson();
            if (stats.hasWarnings()) {
                this.context.logger.warn(stats_1.statsWarningsToString(json, config.stats));
            }
            if (stats.hasErrors()) {
                this.context.logger.error(stats_1.statsErrorsToString(json, config.stats));
            }
        };
        return architect.getBuilderDescription(browserBuilderConfig).pipe(operators_1.concatMap(browserDescription => architect.validateBuilderOptions(browserBuilderConfig, browserDescription)), operators_1.map(browserBuilderConfig => browserBuilderConfig.options), operators_1.concatMap((validatedBrowserOptions) => {
            const browserOptions = validatedBrowserOptions;
            // We need to determine the outFile name so that AngularCompiler can retrieve it.
            let outFile = options.outFile || getI18nOutfile(options.i18nFormat);
            if (options.outputPath) {
                // AngularCompilerPlugin doesn't support genDir so we have to adjust outFile instead.
                outFile = path.join(options.outputPath, outFile);

run(builderConfig: BuilderConfiguration): Observable {
    const options = builderConfig.options;
    const root = this.context.workspace.root;
    const projectRoot = resolve(root, builderConfig.root);
    const host = new virtualFs.AliasHost(this.context.host as virtualFs.Host);
    const webpackBuilder = new WebpackBuilder({ ...this.context, host });

    // TODO: verify using of(null) to kickstart things is a pattern.
    return of(null).pipe(
      concatMap(() => options.deleteOutputPath
        ? this._deleteOutputDir(root, normalize(options.outputPath), this.context.host)
        : of(null)),
        concatMap(() => normalizeFileReplacements(options.fileReplacements, host, root)),
        tap(fileReplacements => options.fileReplacements = fileReplacements),
      concatMap(() => {
        const webpackConfig = this.buildWebpackConfig(root, projectRoot, host, options);

        return webpackBuilder.runWebpack(webpackConfig, getBrowserLoggingCb(options.verbose));
      }),
    );
  }

run(builderConfig: BuilderConfiguration): Observable {
    const options = builderConfig.options;
    const root = this.context.workspace.root;
    const projectRoot = resolve(root, builderConfig.root);
    const host = new virtualFs.AliasHost(this.context.host as virtualFs.Host);
    const webpackBuilder = new WebpackBuilder({ ...this.context, host });

    return of(null).pipe(
      concatMap(() => options.deleteOutputPath
        ? this._deleteOutputDir(root, normalize(options.outputPath), this.context.host)
        : of(null)),
      concatMap(() => normalizeFileReplacements(options.fileReplacements, host, root)),
      tap(fileReplacements => options.fileReplacements = fileReplacements),
      concatMap(() => normalizeAssetPatterns(
        options.assets, host, root, projectRoot, builderConfig.sourceRoot)),
      // Replace the assets in options with the normalized version.
      tap((assetPatternObjects => options.assets = assetPatternObjects)),
      concatMap(() => {
        let webpackConfig;
        try {
          webpackConfig = this.buildWebpackConfig(root, projectRoot, host,
            options as NormalizedBrowserBuilderSchema);

run(builderConfig: BuilderConfiguration): Observable {
    const root = this.context.workspace.root;
    const projectRoot = resolve(root, builderConfig.root);
    const host = new virtualFs.AliasHost(this.context.host as virtualFs.Host);
    const webpackBuilder = new WebpackBuilder({ ...this.context, host });

    const options = normalizeWebpackServerSchema(
      host,
      root,
      resolve(root, builderConfig.root),
      builderConfig.sourceRoot,
      builderConfig.options,
    );

    // TODO: verify using of(null) to kickstart things is a pattern.
    return of(null).pipe(
      concatMap(() => options.deleteOutputPath
        ? this._deleteOutputDir(root, normalize(options.outputPath), this.context.host)
        : of(null)),
      concatMap(() => {
        const webpackConfig = this.buildWebpackConfig(root, projectRoot, host, options);

run(builderConfig) {
        const options = builderConfig.options;
        const root = this.context.workspace.root;
        const projectRoot = core_1.resolve(root, builderConfig.root);
        const host = new core_1.virtualFs.AliasHost(this.context.host);
        const webpackBuilder = new build_webpack_1.WebpackBuilder(Object.assign({}, this.context, { host }));
        return rxjs_1.of(null).pipe(operators_1.concatMap(() => options.deleteOutputPath
            ? this._deleteOutputDir(root, core_1.normalize(options.outputPath), this.context.host)
            : rxjs_1.of(null)), operators_1.concatMap(() => utils_1.normalizeFileReplacements(options.fileReplacements, host, root)), operators_1.tap(fileReplacements => options.fileReplacements = fileReplacements), operators_1.concatMap(() => utils_1.normalizeAssetPatterns(options.assets, host, root, projectRoot, builderConfig.sourceRoot)), 
        // Replace the assets in options with the normalized version.
        operators_1.tap((assetPatternObjects => options.assets = assetPatternObjects)), operators_1.concatMap(() => {
            let webpackConfig;
            try {
                webpackConfig = this.buildWebpackConfig(root, projectRoot, host, options);
            }
            catch (e) {
                return rxjs_1.throwError(e);
            }
            return webpackBuilder.runWebpack(webpackConfig, exports.getBrowserLoggingCb(options.verbose));
        }), operators_1.concatMap(buildEvent => {
            if (buildEvent.success && !options.watch && options.serviceWorker) {
                return new rxjs_1.Observable(obs => {

run(builderConfig) {
        const root = this.context.workspace.root;
        const projectRoot = core_1.resolve(root, builderConfig.root);
        const host = new core_1.virtualFs.AliasHost(this.context.host);
        const webpackBuilder = new build_webpack_1.WebpackBuilder(Object.assign({}, this.context, { host }));
        const options = utils_1.normalizeBuilderSchema(host, root, builderConfig);
        // TODO: verify using of(null) to kickstart things is a pattern.
        return rxjs_1.of(null).pipe(operators_1.concatMap(() => options.deleteOutputPath
            ? this._deleteOutputDir(root, core_1.normalize(options.outputPath), this.context.host)
            : rxjs_1.of(null)), operators_1.concatMap(() => {
            const webpackConfig = this.buildWebpackConfig(root, projectRoot, host, options);
            return webpackBuilder.runWebpack(webpackConfig, browser_1.getBrowserLoggingCb(options.verbose));
        }));
    }
    buildWebpackConfig(root, projectRoot, host, options) {

constructor(private context: BuilderContext) {
    this.webpackBuilder = new WebpackBuilder(this.context);
    this.root = getSystemPath(this.context.workspace.root);
  }

protected createWebpackBuilder(context: BuilderContext): WebpackBuilder {
    return new WebpackBuilder(context);
  }