fix(@angular/cli): fix eval-sourcemap when sourcemap is undefined

Also add test to ensure it doesn't break.

Followup to #7919

Author: filipesilva

packages/@angular/cli/commands/serve.ts

@@ -135,11 +135,8 @@ const ServeCommand = Command.extend({
       commandOptions.vendorChunk = !commandOptions.buildOptimizer;
     }
 
-    // Default evalSourcemaps to true when sourcemaps are true.
-    // This makes rebuilds faster.
-    if (commandOptions.sourcemaps === true) {
-      commandOptions.evalSourcemaps = true;
-    }
+    // Default evalSourcemaps to true for serve. This makes rebuilds faster.
+    commandOptions.evalSourcemaps = true;
 
     return checkPort(commandOptions.port, commandOptions.host, defaultPort)
       .then(port => {

tests/e2e/tests/build/eval-sourcemap.ts

@@ -0,0 +1,24 @@
+import {execAndWaitForOutputToMatch, killAllProcesses} from '../../utils/process';
+import {getGlobalVariable} from '../../utils/env';
+
+
+export default function() {
+  // Skip this in ejected tests.
+  if (getGlobalVariable('argv').eject) {
+    return Promise.resolve();
+  }
+
+  return Promise.resolve()
+    // Check that ng serve has eval sourcemaps by default.
+    .then(() => execAndWaitForOutputToMatch('ng', ['serve'], /webpack: Compiled successfully/))
+    .then((output) => {
+      const stdout = output.stdout;
+      if (/\.js\.map/.test(stdout)) {
+        throw new Error('Expected eval sourcemap but file sourcemap was present instead.');
+      }
+    })
+    .then(() => killAllProcesses(), (err: any) => {
+      killAllProcesses();
+      throw err;
+    });
+}