Use ByteArray's native for Socket and File.

runtime/bin/file_impl.dart

Index: runtime/bin/file_impl.dart
===================================================================
--- runtime/bin/file_impl.dart	(revision 3621)
+++ runtime/bin/file_impl.dart	(working copy)
@@ -19,10 +19,10 @@
   }
 
   List<int> _read(int bytesToRead) {
-    List<int> result = new List<int>(bytesToRead);
+    List<int> result = new ByteArray(bytesToRead);
     int bytesRead = _file.readListSync(result, 0, bytesToRead);
     if (bytesRead < bytesToRead) {
-      List<int> buffer = new List<int>(bytesRead);
+      List<int> buffer = new ByteArray(bytesRead);
       buffer.copyFrom(result, 0, 0, bytesRead);
       result = buffer;
     }
@@ -175,7 +175,7 @@
                       port.toSendPort());
       return;
     }
-    var buffer = new List(_bytes);
+    var buffer = new ByteArray(_bytes);
     var result =
         new _ReadListResult(_FileUtils.readList(_id, buffer, 0, _bytes),
                             buffer);
@@ -424,12 +424,14 @@
     // When using the Dart C API access to ObjectArray by index is
     // currently much faster. This function will make a copy of the
     // supplied List to an ObjectArray if it isn't already.
-    ObjectArray outBuffer;
+    List<int> outBuffer;
     int outOffset = offset;
     if (buffer is ObjectArray) {
       outBuffer = buffer;
+    } else if (buffer is ByteArray) {
+      outBuffer = buffer;
     } else {
-      outBuffer = new ObjectArray(bytes);
+      outBuffer = new ByteArray(bytes);
       outOffset = 0;
       int j = offset;
       for (int i = 0; i < bytes; i++) {