Redo the interface for capture stdio.

runtime/bin/embedded_dart_io.h

Index: runtime/bin/embedded_dart_io.h
diff --git a/runtime/bin/embedded_dart_io.h b/runtime/bin/embedded_dart_io.h
index e19b21ac8d1f968421795a789351ec94d6bf530e..4d7dbae14cc346df9c0c8c7bf9e50fe5af0d2ba5 100644
--- a/runtime/bin/embedded_dart_io.h
+++ b/runtime/bin/embedded_dart_io.h
@@ -11,6 +11,19 @@ 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