Remove DirectoryException and LinkException from dart:io and use FileException instaed.

sdk/lib/_internal/pub/lib/src/io.dart

Index: sdk/lib/_internal/pub/lib/src/io.dart
diff --git a/sdk/lib/_internal/pub/lib/src/io.dart b/sdk/lib/_internal/pub/lib/src/io.dart
index 55827c1f63cb207b5ad642d943f2d3072687a3a6..b4f6d919b01131f4e8f233ea2fa909963f73f649 100644
--- a/sdk/lib/_internal/pub/lib/src/io.dart
+++ b/sdk/lib/_internal/pub/lib/src/io.dart
@@ -216,7 +216,7 @@ String ensureDir(String dirPath) {
 
   try {
     createDir(dirPath);
-  } on DirectoryException catch (ex) {
+  } on FileSystemException catch (ex) {
     // Error 17 means the directory already exists (or 183 on Windows).
     if (ex.osError.errorCode == 17 || ex.osError.errorCode == 183) {
       log.fine("Got 'already exists' error when creating directory.");