Use ByteArray's native for Socket and File.

runtime/bin/socket_impl.dart

Index: runtime/bin/socket_impl.dart
===================================================================
--- runtime/bin/socket_impl.dart	(revision 3811)
+++ runtime/bin/socket_impl.dart	(working copy)
@@ -306,19 +306,24 @@
       if ((offset + bytes) > buffer.length) {
         throw new IndexOutOfRangeException(offset + bytes);
       }
-      // When using the Dart C API access to ObjectArray by index is
+      // 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 an ObjectArray if it isn't already.
-      ObjectArray outBuffer;
+      // supplied List to a ByteArray if it isn't already.
+      List outBuffer;
       int outOffset = offset;
-      if (buffer is ObjectArray) {
+      if (buffer is ByteArray || buffer is ObjectArray) {
         outBuffer = buffer;
       } else {
-        outBuffer = new ObjectArray(bytes);
+        outBuffer = new ByteArray(bytes);
         outOffset = 0;
         int j = offset;
         for (int i = 0; i < bytes; i++) {
-          outBuffer[i] = buffer[j];
+          int value = buffer[j];
+          if (value is! int) {
+            throw new FileIOException(
+                "List element is not an integer at index $j");
+          }
+          outBuffer[i] = value;
           j++;
         }
       }