Use SetReturnUnsafe in dart_api_impl.cc.

vm/native_arguments.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_NATIVE_ARGUMENTS_H_
 #define VM_NATIVE_ARGUMENTS_H_
 
 #include "platform/assert.h"
 #include "vm/globals.h"
 #include "vm/stub_code.h"
@@ skipping 21 matching lines @@
          (Utils::IsAligned(current_sp, OS::ActivationFrameAlignment())));      \
 }
 #endif
 
 #else
 
 #define CHECK_STACK_ALIGNMENT { }
 
 #endif
 
+DART_EXTERN_C {
+  void Dart_SetReturnValue(Dart_NativeArguments, Dart_Handle);
+}
 
 // Class NativeArguments is used to access arguments passed in from
 // generated dart code to a runtime function or a dart library native
 // function. It is also used to set the return value if any at the slot
 // reserved for return values.
 // All runtime function/dart library native functions have the
 // following signature:
 //   void function_name(NativeArguments arguments);
 // Inside the function, arguments are accessed as follows:
 //   const Type& arg1 = Type::CheckedHandle(arguments.GetArgument(0));
@@ skipping 19 matching lines @@
     return OFFSET_OF(NativeArguments, isolate_);
   }
   static intptr_t argc_offset() { return OFFSET_OF(NativeArguments, argc_); }
   static intptr_t argv_offset() { return OFFSET_OF(NativeArguments, argv_); }
   static intptr_t retval_offset() {
     return OFFSET_OF(NativeArguments, retval_);
   }
 
  private:
   friend class BootstrapNatives;
+  friend void Dart_SetReturnValue(Dart_NativeArguments, Dart_Handle);
 
   // Since this function is passed a RawObject directly, we need to be
   // exceedingly careful when we use it.  If there are any other side
   // effects in the statement that may cause GC, it could lead to
   // bugs.
   void SetReturnUnsafe(RawObject* value) const;
 
   Isolate* isolate_;  // Current isolate pointer.
   int argc_;  // Number of arguments passed to the runtime call.
   RawObject*(*argv_)[];  // Pointer to an array of arguments to runtime call.
   RawObject** retval_;  // Pointer to the return value area.
 };
 
 }  // namespace dart
 
 #endif  // VM_NATIVE_ARGUMENTS_H_