build: run e2e tests with bazel (#14656)

* Builds the e2e app with Bazel
* Serves the e2e app with Bazel
* Runs the e2e tests with Bazel protractor rules

e2e/start-devserver.js

@@ -0,0 +1,42 @@
+const protractor = require('protractor');
+const utils = require('@angular/bazel/protractor-utils');
+const spawn = require('child_process').spawn;
+
+/**
+ * Runs the specified server binary from a given workspace and waits for the server
+ * being ready. The server binary will be resolved from the runfiles.
+ */
+async function runBazelServer(workspace, serverPath, timeout) {
+  const serverBinary = require.resolve(`${workspace}/${serverPath}`);
+  const port = await utils.findFreeTcpPort();
+
+  // Start the Bazel server binary with a random free TCP port.
+  const serverProcess = spawn(serverBinary, ['-port', port], {stdio: 'inherit'});
+
+  // In case the process exited with an error, we want to propagate the error.
+  serverProcess.on('exit', exitCode => {
+    if (exitCode !== 0) {
+      throw new Error(`Server exited with error code: ${exitCode}`);
+    }
+  });
+
+  // Wait for the server to be bound to the given port.
+  await utils.waitForServer(port, timeout);
+
+  return port;
+}
+
+/**
+ * Called by Protractor before starting any tests. This is script is responsible for
+ * starting up the devserver and updating the Protractor base URL to the proper port.
+ */
+module.exports = async function(config) {
+  const port = await runBazelServer(config.workspace, config.server);
+  const baseUrl = `http://localhost:${port}`;
+  const processedConfig = await protractor.browser.getProcessedConfig();
+
+  // Update the protractor "baseUrl" to match the new random TCP port. We need random TCP ports
+  // because otherwise Bazel could not execute protractor tests concurrently.
+  protractor.browser.baseUrl = baseUrl;
+  processedConfig.baseUrl = baseUrl;
+};