feat(@angular/cli): copy safety SW from NPM on SW build

Deploying apps with service workers can be tricky. This commit has
the CLI copy the safety-worker.js file from @angular/service-worker
(if it's present) into the dist/ directory of the bundled app, both
providing a quick option for developers who need to deactivate an
already installed worker. It also copies the file into the path
dist/worker-basic.min.js, used by apps built on the previous SW.
Once a SW path is deployed on the web, it needs to be served until
all users have migrated off of that path.

Author: alxhub

Diff for: packages/@angular/cli/utilities/service-worker/index.ts

@@ -70,6 +70,7 @@ export function augmentAppWithServiceWorker(projectRoot: string, appRoot: string
     outputPath: string, baseHref: string): Promise<void> {
   // Path to the worker script itself.
   const workerPath = resolveProjectModule(projectRoot, '@angular/service-worker/ngsw-worker.js');
+  const safetyPath = path.join(path.dirname(workerPath), 'safety-worker.js');
   const configPath = path.resolve(appRoot, 'ngsw-config.json');
 
   if (!fs.existsSync(configPath)) {
@@ -89,5 +90,12 @@ export function augmentAppWithServiceWorker(projectRoot: string, appRoot: string
       // Copy worker script to dist directory.
       const workerCode = fs.readFileSync(workerPath);
       fs.writeFileSync(path.resolve(outputPath, 'ngsw-worker.js'), workerCode);
+
+      // If @angular/service-worker has the safety script, copy it into two locations.
+      if (fs.existsSync(safetyPath)) {
+        const safetyCode = fs.readFileSync(safetyPath);
+        fs.writeFileSync(path.resolve(outputPath, 'worker-basic.min.js'), safetyCode);
+        fs.writeFileSync(path.resolve(outputPath, 'safety-worker.js'), safetyCode);
+      }
     });
 }

Diff for: tests/e2e/tests/build/service-worker.ts

@@ -42,6 +42,10 @@ export default function() {
     .then(() => expectFileToMatch('dist/ngsw.json', /"\/foo\/bar\/index.html"/))
     .then(() => ng('build', '--prod', '--service-worker=false'))
     .then(() => expectFileNotToExist('dist/ngsw.json'))
+    .then(() => writeFile('node_modules/@angular/service-worker/safety-worker.js', 'false'))
+    .then(() => ng('build', '--prod'))
+    .then(() => expectFileToExist('dist/safety-worker.js'))
+    .then(() => expectFileToExist('dist/worker-basic.min.js'))
     .then(() => ng('eject', '--prod'))
     .then(() => silentNpm('install'))
     .then(() => npm('run', 'build'))