fix #27771, create directory if needed

pkg/dev_compiler/test/worker/worker_test.dart

Index: pkg/dev_compiler/test/worker/worker_test.dart
diff --git a/pkg/dev_compiler/test/worker/worker_test.dart b/pkg/dev_compiler/test/worker/worker_test.dart
index 6ad4c052c5b7898afff10a5ee25f384335f2e08d..daa1841b7268d455ffd2b7e3fefd1dea96efa617 100644
--- a/pkg/dev_compiler/test/worker/worker_test.dart
+++ b/pkg/dev_compiler/test/worker/worker_test.dart
@@ -16,7 +16,7 @@ main() {
   group('Hello World', () {
     final argsFile = new File('test/worker/hello_world.args').absolute;
     final inputDartFile = new File('test/worker/hello_world.dart').absolute;
-    final outputJsFile = new File('test/worker/hello_world.js').absolute;
+    final outputJsFile = new File('test/worker/out/hello_world.js').absolute;
     final dartSdkSummary = new File('lib/sdk/ddc_sdk.sum').absolute;
     final executableArgs = ['bin/dartdevc.dart'];
     final compilerArgs = [
@@ -36,7 +36,9 @@ main() {
 
     tearDown(() {
       if (inputDartFile.existsSync()) inputDartFile.deleteSync();
-      if (outputJsFile.existsSync()) outputJsFile.deleteSync();
+      if (outputJsFile.parent.existsSync()) {
+        outputJsFile.parent.deleteSync(recursive: true);

[kevmoo, 2016/11/08 02:51:30]

Huh? This seems – bad.

Are we sure this directory is empty?

[Jennifer Messerly, 2016/11/08 18:11:51]

it's a test folder, so yes (we're in "worker_test.dart"). I'm happy to make it
more defensive somehow, if you have suggestions.

[kevmoo, 2016/11/08 18:16:47]

*sigh* Sorry. Paranoid. :-)

+      }
       if (argsFile.existsSync()) argsFile.deleteSync();
     });