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/sourcemap.ts

@@ -1,4 +1,4 @@
-import {ng} from '../../utils/process';
+import {ng, execAndWaitForOutputToMatch} from '../../utils/process';
 import {expectFileToExist} from '../../utils/fs';
 import {expectToFail} from '../../utils/utils';
 import {getGlobalVariable} from '../../utils/env';
@@ -20,5 +20,15 @@ export default function() {
     .then(() => expectToFail(() => expectFileToExist('dist/main.bundle.js.map')))
 
     .then(() => ng('build', '--prod', '--output-hashing=none', '--sourcemap'))
-    .then(() => expectFileToExist('dist/main.bundle.js.map'));
+    .then(() => expectFileToExist('dist/main.bundle.js.map'))
+
+    // 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.');
+      }
+    })
+    ;
 }