Add temporary directory for dartc compilation of tests.

tests/stub-generator/test_config.dart

Index: tests/stub-generator/test_config.dart
diff --git a/tests/stub-generator/test_config.dart b/tests/stub-generator/test_config.dart
index 4eb9e1e2716c675b8164e60dbbf3114a9f458493..e57ce66f9555cf2830e3d233fd853c9236c88731 100644
--- a/tests/stub-generator/test_config.dart
+++ b/tests/stub-generator/test_config.dart
@@ -21,6 +21,8 @@ class StubGeneratorTestSuite extends StandardTestSuite {
     }
   }
 
+  bool get requiresCleanTemporaryDirectory() => true;
+
   void combineFiles(String filename,
                     String stubsFile,
                     Function onGenerated) {
@@ -99,8 +101,8 @@ class StubGeneratorTestSuite extends StandardTestSuite {
                         String classes,
                         Function onGenerated) {
     testGeneratorStarted();
-    Directory temp = new Directory('');
-    temp.createTempSync();
+    Directory temp = createOutputDirectory(interfaceFile, '');
+
     File stubsOutFile = new File("${temp.path}/${interfaceFile}");
     stubsOutFile.createSync();
     String stubsPath = stubsOutFile.fullPathSync();