Performance improvement for the Dart VM runtime method

runtime/vm/raw_object.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_RAW_OBJECT_H_
 #define VM_RAW_OBJECT_H_
 
 #include "platform/assert.h"
 #include "vm/globals.h"
 #include "vm/token.h"
@@ skipping 1105 matching lines @@
     return peer_;
   }
 
  private:
   const T* data_;
   void* peer_;
   Dart_PeerFinalizer callback_;
 };
 
 
+DART_EXTERN_C {
+  Dart_Handle Dart_ExternalStringGetPeer(Dart_Handle, void**);
+}
+
+
 class RawExternalOneByteString : public RawString {
   RAW_HEAP_OBJECT_IMPLEMENTATION(ExternalOneByteString);
 
   ExternalStringData<uint8_t>* external_data_;
+  friend Dart_Handle Dart_ExternalStringGetPeer(Dart_Handle, void**);
 };
 
 
 class RawExternalTwoByteString : public RawString {
   RAW_HEAP_OBJECT_IMPLEMENTATION(ExternalTwoByteString);
 
   ExternalStringData<uint16_t>* external_data_;
+  friend Dart_Handle Dart_ExternalStringGetPeer(Dart_Handle, void**);
 };
 
 
 class RawExternalFourByteString : public RawString {
   RAW_HEAP_OBJECT_IMPLEMENTATION(ExternalFourByteString);
 
   ExternalStringData<uint32_t>* external_data_;
+  friend Dart_Handle Dart_ExternalStringGetPeer(Dart_Handle, void**);
 };
 
 
 class RawBool : public RawInstance {
   RAW_HEAP_OBJECT_IMPLEMENTATION(Bool);
 
   bool value_;
 };
 
 
@@ skipping 426 matching lines @@
          kExternalUint64ArrayCid == kByteArrayCid + 18 &&
          kExternalFloat32ArrayCid == kByteArrayCid + 19 &&
          kExternalFloat64ArrayCid == kByteArrayCid + 20 &&
          kStacktraceCid == kByteArrayCid + 21);
   return (index >= kByteArrayCid && index <= kExternalFloat64ArrayCid);
 }
 
 }  // namespace dart
 
 #endif  // VM_RAW_OBJECT_H_