Split dart:builtin into dart:builtin and dart:io.

runtime/bin/builtin_impl_sources.gypi

Index: runtime/bin/builtin_impl_sources.gypi
diff --git a/runtime/bin/builtin_sources.gypi b/runtime/bin/builtin_impl_sources.gypi
similarity index 65%
copy from runtime/bin/builtin_sources.gypi
copy to runtime/bin/builtin_impl_sources.gypi
index 8147e83ecfa9cbd68289a834d27a8085378e7d9c..523d1b61459d6646c55121d43ef58f32a1c45ad9 100644
--- a/runtime/bin/builtin_sources.gypi
+++ b/runtime/bin/builtin_impl_sources.gypi
@@ -2,38 +2,10 @@
 # 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.
 
-# This file contains all sources (vm and tests) for the dart virtual machine.
-# Unit test files need to have a '_test' suffix appended to the name.
+# This file contains all C++ sources for the dart:builtin and dart:io
+# libraries.
 {
   'sources': [
-    #
-    # Dart sources.
-    #
-    'builtin.dart',
-    'buffer_list.dart',
-    'chunked_stream.dart',
-    'directory.dart',
-    'directory_impl.dart',
-    'eventhandler.dart',
-    'file.dart',
-    'file_impl.dart',
-    'input_stream.dart',
-    'list_stream.dart',
-    'output_stream.dart',
-    'stream_util.dart',
-    'string_stream.dart',
-    'platform.dart',
-    'platform_impl.dart',
-    'process.dart',
-    'process_impl.dart',
-    'socket.dart',
-    'socket_impl.dart',
-    'socket_stream.dart',
-    'timer.dart',
-    'timer_impl.dart',
-    #
-    # C++ sources.
-    #
     'dartutils.cc',
     'dartutils.h',
     'directory.cc',