Reapply change to use system code page on Windows to fix Pub.

sdk/lib/_internal/compiler/implementation/lib/io_patch.dart

Index: sdk/lib/_internal/compiler/implementation/lib/io_patch.dart
diff --git a/sdk/lib/_internal/compiler/implementation/lib/io_patch.dart b/sdk/lib/_internal/compiler/implementation/lib/io_patch.dart
index 7a87745dff70da61181226b798a00dbdaa94d2d4..9b677d6c20e98b784ce5c2fe650a4f818b119b3f 100644
--- a/sdk/lib/_internal/compiler/implementation/lib/io_patch.dart
+++ b/sdk/lib/_internal/compiler/implementation/lib/io_patch.dart
@@ -192,3 +192,15 @@ patch class _StdIOUtils {
     throw new UnsupportedError("StdIOUtils._getStdioHandleType");
   }
 }
+
+patch class _WindowsCodePageDecoder {
+  patch static String _decodeBytes(List<int> bytes) {
+    throw new UnsupportedError("_WindowsCodePageDecoder._decodeBytes");
+  }
+}
+
+patch class _WindowsCodePageEncoder {
+  patch static List<int> _encodeString(String string) {
+    throw new UnsupportedError("_WindowsCodePageEncoder._encodeString");
+  }
+}