Revert "Fix remaining strong-mode warnings and errors in dart:io."

sdk/lib/io/data_transformer.dart

Index: sdk/lib/io/data_transformer.dart
diff --git a/sdk/lib/io/data_transformer.dart b/sdk/lib/io/data_transformer.dart
index 6a50af49f80c3c676dcde2ca3ce9e56c7e62ea3d..968fd20ebcbb8d2c83f99666e4dc434b7046cf8f 100644
--- a/sdk/lib/io/data_transformer.dart
+++ b/sdk/lib/io/data_transformer.dart
@@ -492,7 +492,7 @@ class _FilterSink extends ByteConversionSink {
       _filter.process(bufferAndStart.buffer,
                       bufferAndStart.start,
                       end - (start - bufferAndStart.start));
-      List<int> out;
+      var out;
       while ((out = _filter.processed(flush: false)) != null) {
         _sink.add(out);
       }
@@ -510,7 +510,7 @@ class _FilterSink extends ByteConversionSink {
     // message would not have a GZip frame (if compressed with GZip).
     if (_empty) _filter.process(const [], 0, 0);
     try {
-      List<int> out;
+      var out;
       while ((out = _filter.processed(end: true)) != null) {
         _sink.add(out);
       }