Fix Socket_WriteList to use the offset for external byte arrays.

runtime/bin/socket.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "bin/io_buffer.h"
 #include "bin/socket.h"
 #include "bin/dartutils.h"
 #include "bin/thread.h"
 #include "bin/utils.h"
 
@@ skipping 168 matching lines @@
   }
 
   intptr_t total_bytes_written = 0;
   intptr_t bytes_written = 0;
   if (Dart_IsByteArrayExternal(buffer_obj)) {
     void* buffer = NULL;
     result = Dart_ExternalByteArrayGetData(buffer_obj, &buffer);
     if (Dart_IsError(result)) {
       Dart_PropagateError(result);
     }
+    buffer = static_cast<void*>((static_cast<uint8_t*>(buffer) + offset));
     bytes_written = Socket::Write(socket, buffer, length);
     if (bytes_written > 0) total_bytes_written = bytes_written;
   } else {
     // Send data in chunks of maximum 16KB.
     const intptr_t max_chunk_length =
         dart::Utils::Minimum(length, static_cast<intptr_t>(16 * KB));
     uint8_t* buffer = new uint8_t[max_chunk_length];
     do {
       intptr_t chunk_length =
           dart::Utils::Minimum(max_chunk_length, length - total_bytes_written);
@@ skipping 232 matching lines @@
 
 
 Dart_Handle Socket::SetSocketIdNativeField(Dart_Handle socket, intptr_t id) {
   return Dart_SetNativeInstanceField(socket, kSocketIdNativeField, id);
 }
 
 
 Dart_Handle Socket::GetSocketIdNativeField(Dart_Handle socket, intptr_t* id) {
   return Dart_GetNativeInstanceField(socket, kSocketIdNativeField, id);
 }