Reapply change to hide VM-only List implementation classes.

runtime/bin/socket_impl.dart

Index: runtime/bin/socket_impl.dart
diff --git a/runtime/bin/socket_impl.dart b/runtime/bin/socket_impl.dart
index 49654130d1132e1aeac09c08c10343097025d226..3cd2c770f1cc6a8b7de41ace2b18d256f6beb8f4 100644
--- a/runtime/bin/socket_impl.dart
+++ b/runtime/bin/socket_impl.dart
@@ -404,28 +404,8 @@ class _Socket extends _SocketBase implements Socket {
       if ((offset + bytes) > buffer.length) {
         throw new IndexOutOfRangeException(offset + bytes);
       }
-      // When using the Dart C API to access raw data, using a ByteArray is
-      // currently much faster. This function will make a copy of the
-      // supplied List to a ByteArray if it isn't already.
-      List outBuffer;
-      int outOffset = offset;
-      if (buffer is Uint8List || buffer is ObjectArray) {
-        outBuffer = buffer;
-      } else {
-        outBuffer = new Uint8List(bytes);
-        outOffset = 0;
-        int j = offset;
-        for (int i = 0; i < bytes; i++) {
-          int value = buffer[j];
-          if (value is! int) {
-            throw new FileIOException(
-                "List element is not an integer at index $j");
-          }
-          outBuffer[i] = value;
-          j++;
-        }
-      }
-      var result = _writeList(outBuffer, outOffset, bytes);
+      var fastBuffer = _ensureFastAndSerializableBuffer(buffer, offset, bytes);
+      var result = _writeList(fastBuffer[0], fastBuffer[1], bytes);
       if (result is OSError) {
         _reportError(result, "Write failed");
         // If writing fails we return 0 as the number of bytes and