Redo the interface for capture stdio.

runtime/bin/embedded_dart_io.h

 // Copyright (c) 2015, 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.
 
 #ifndef BIN_EMBEDDED_DART_IO_H_
 #define BIN_EMBEDDED_DART_IO_H_
 
 namespace dart {
 namespace bin {
 
 // Bootstraps 'dart:io'.
 void BootstrapDartIo();
 
+// Tells the system whether to capture Stdout events.
+void SetCaptureStdout(bool value);
+
+// Tells the system whether to capture Stderr events.
+void SetCaptureStderr(bool value);
+
+// Should Stdout events be captured?
+bool ShouldCaptureStdout();
+
+// Should Stderr events be captured?
+bool ShouldCaptureStderr();
+
+
 }  // namespace bin
 }  // namespace dart
 
 #endif  // BIN_EMBEDDED_DART_IO_H_