Provide access to stdin, stdout and stderr

runtime/bin/process_impl.dart

Index: runtime/bin/process_impl.dart
diff --git a/runtime/bin/process_impl.dart b/runtime/bin/process_impl.dart
index 4cb462b4fe954c1cd02bd843675f3a3b678639c5..1e121eefc82ec5fa45ac72b1b0948d9f2a862fc2 100644
--- a/runtime/bin/process_impl.dart
+++ b/runtime/bin/process_impl.dart
@@ -29,9 +29,9 @@ class _Process implements Process {
       _arguments[i] = arguments[i];
     }
 
-    _in = new _Socket._internalOutputOnly();
-    _out = new _Socket._internalInputOnly();
-    _err = new _Socket._internalOutputOnly();
+    _in = new _Socket._internalReadOnly();  // stdout coming from process.
+    _out = new _Socket._internalWriteOnly();  // stdin going to process.
+    _err = new _Socket._internalReadOnly();  // stderr coming from process.
     _exitHandler = new _Socket._internal();
     _closed = false;
     _killed = false;