Fix standalone tests that didn't delete the temporary directories they created.

tests/standalone/src/StreamPipeTest.dart

Index: tests/standalone/src/StreamPipeTest.dart
diff --git a/tests/standalone/src/StreamPipeTest.dart b/tests/standalone/src/StreamPipeTest.dart
index 19890175ace80a3b79fc87c67bb55a2d616dc06d..93082a21e6905ced625815e95325750c95f070bf 100644
--- a/tests/standalone/src/StreamPipeTest.dart
+++ b/tests/standalone/src/StreamPipeTest.dart
@@ -96,6 +96,7 @@ class PipeServerGame {
           // file.
           bool result = compareFileContent(srcFileName, dstFileName);
           new File(dstFileName).deleteSync();
+          tempDir.deleteSync();
           Expect.isTrue(result);
 
           _socket.close();
@@ -170,6 +171,7 @@ testFileToFilePipe1() {
   srcStream.closeHandler = () {
     bool result = compareFileContent(srcFileName, dstFileName);
     new File(dstFileName).deleteSync();
+    tempDir.deleteSync();
     Expect.isTrue(result);
   };
 
@@ -210,6 +212,7 @@ testFileToFilePipe2() {
     src.closeSync();
     dst.closeSync();
     dstFile.deleteSync();
+    tempDir.deleteSync();
   };
 
   srcStream.pipe(dstStream, close: false);
@@ -249,6 +252,7 @@ testFileToFilePipe3() {
       src.closeSync();
       dst.closeSync();
       dstFile.deleteSync();
+      tempDir.deleteSync();
     };
 
     // Pipe another copy of the source file.