build: prevent binding BrowserSync UI server during test execution (#23733)

Author: Marco Marche

tools/dev-server/dev-server.ts

@@ -38,8 +38,12 @@ export class DevServer {
   };
 
   constructor(
-      readonly port: number, private _rootPaths: string[],
-      private _historyApiFallback: boolean = false) {}
+      readonly port: number, private _rootPaths: string[], bindUi: boolean,
+      private _historyApiFallback: boolean = false) {
+    if (bindUi === false) {
+      this.options.ui = false;
+    }
+  }
 
   /** Starts the server on the given port. */
   start() {

tools/dev-server/main.ts

@@ -16,12 +16,12 @@ const {root_paths: _rootPathsRaw, port, historyApiFallback} =
     minimist(args, {boolean: 'historyApiFallback'});
 const rootPaths = _rootPathsRaw ? _rootPathsRaw.split(',') : ['/'];
 
-const server = new DevServer(port, rootPaths, historyApiFallback);
+const bindUi = process.env.TEST_TARGET === undefined;
+const server = new DevServer(port, rootPaths, bindUi, historyApiFallback);
 
 // Setup ibazel support.
 setupBazelWatcherSupport(server);
 
 // Start the devserver. The server will always bind to the loopback and
 // the public interface of the current host.
 server.start();
-