Add optimized String.fromCharCodes path for Uint8List and Int8List.

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 78 matching lines @@
   V(List_getIndexed, 2)                                                        \
   V(List_setIndexed, 3)                                                        \
   V(List_getLength, 1)                                                         \
   V(List_copyFromObjectArray, 5)                                               \
   V(StringBase_createFromCodePoints, 1)                                        \
   V(StringBase_substringUnchecked, 3)                                          \
   V(StringBuffer_createStringFromUint16Array, 3)                               \
   V(OneByteString_substringUnchecked, 3)                                       \
   V(OneByteString_splitWithCharCode, 2)                                        \
   V(OneByteString_allocate, 1)                                                 \
+  V(OneByteString_allocateFromOneByteList, 1)                                  \
   V(OneByteString_setAt, 3)                                                    \
   V(ExternalOneByteString_getCid, 0)                                           \
   V(String_getHashCode, 1)                                                     \
   V(String_getLength, 1)                                                       \
   V(String_charAt, 2)                                                          \
   V(String_codeUnitAt, 2)                                                      \
   V(String_concat, 2)                                                          \
   V(String_fromEnvironment, 3)                                                 \
   V(String_toLowerCase, 1)                                                     \
   V(String_toUpperCase, 1)                                                     \
@@ skipping 216 matching lines @@
   static void DN_##name(Dart_NativeArguments args);
 
   BOOTSTRAP_NATIVE_LIST(DECLARE_BOOTSTRAP_NATIVE)
 
 #undef DECLARE_BOOTSTRAP_NATIVE
 };
 
 }  // namespace dart
 
 #endif  // VM_BOOTSTRAP_NATIVES_H_