Avoid UTF-8 decoding in num.toString.

runtime/vm/bootstrap_natives.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 VM_BOOTSTRAP_NATIVES_H_
 #define VM_BOOTSTRAP_NATIVES_H_
 
 #include "vm/native_entry.h"
 
 // bootstrap dart natives used in the core dart library.
@@ skipping 352 matching lines @@
   V(Uri_isWindowsPlatform, 0)                                                  \
   V(LibraryPrefix_load, 1)                                                     \
   V(LibraryPrefix_invalidateDependentCode, 1)                                  \
   V(LibraryPrefix_loadError, 1)                                                \
   V(UserTag_new, 2)                                                            \
   V(UserTag_label, 1)                                                          \
   V(UserTag_defaultTag, 0)                                                     \
   V(UserTag_makeCurrent, 1)                                                    \
   V(Profiler_getCurrentTag, 0)                                                 \
   V(ClassID_getID, 1)                                                          \
+  V(Num_toString, 1)                                                           \
 
 
 class BootstrapNatives : public AllStatic {
  public:
   static Dart_NativeFunction Lookup(Dart_Handle name,
                                     int argument_count,
                                     bool* auto_setup_scope);
 
   static const uint8_t* Symbol(Dart_NativeFunction* nf);
 
 #define DECLARE_BOOTSTRAP_NATIVE(name, ignored)                                \
   static void DN_##name(Dart_NativeArguments args);
 
   BOOTSTRAP_NATIVE_LIST(DECLARE_BOOTSTRAP_NATIVE)
 
 #undef DECLARE_BOOTSTRAP_NATIVE
 };
 
 }  // namespace dart
 
 #endif  // VM_BOOTSTRAP_NATIVES_H_