Always mark stdout as blocking when using 'print'.

runtime/bin/platform.h

 // Copyright (c) 2012, 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_PLATFORM_H_
 #define BIN_PLATFORM_H_
 
 #include "bin/builtin.h"
 
 
@@ skipping 44 matching lines @@
     script_index_ = script_index;
     argv_ = argv;
   }
   static int GetScriptIndex() {
     return script_index_;
   }
   static char** GetArgv() {
     return argv_;
   }
 
+  static void PrintBlocking(FILE* file, const char* format, ...)
+      PRINTF_ATTRIBUTE(2, 3);
+
  private:
   static const char* executable_name_;
   static const char* package_root_;
   static int script_index_;
   static char** argv_;  // VM flags are argv_[1 ... script_index_ - 1]
 
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(Platform);
 };
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // BIN_PLATFORM_H_