Dart_SetReturnValue now accepts and propagates error handles.

runtime/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 "platform/memory_sanitizer.h"
 #include "vm/globals.h"
@@ skipping 113 matching lines @@
     }
     int function_bits = FunctionBits::decode(argc_tag_);
     const int actual_index = index + NumHiddenArgs(function_bits);
     return ArgAt(actual_index);
   }
 
   void SetReturn(const Object& value) const {
     *retval_ = value.raw();
   }
 
+  RawObject* ReturnValue() const {
+    return *retval_;
+  }
+
   static intptr_t thread_offset() {
     return OFFSET_OF(NativeArguments, thread_);
   }
   static intptr_t argc_tag_offset() {
     return OFFSET_OF(NativeArguments, argc_tag_);
   }
   static intptr_t argv_offset() { return OFFSET_OF(NativeArguments, argv_); }
   static intptr_t retval_offset() {
     return OFFSET_OF(NativeArguments, retval_);
   }
@@ skipping 83 matching lines @@
 
   Thread* thread_;  // Current thread pointer.
   int argc_tag_;  // Encodes argument count and invoked native call type.
   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_