Use the distinguished class, ApiFailure, to signal when a Dart_Result is

runtime/vm/raw_object.h

 // Copyright (c) 2011, 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 "vm/assert.h"
 #include "vm/globals.h"
 #include "vm/snapshot.h"
@@ skipping 19 matching lines @@
   V(Script)                                                                    \
   V(Library)                                                                   \
   V(LibraryPrefix)                                                             \
   V(Code)                                                                      \
   V(Instructions)                                                              \
   V(PcDescriptors)                                                             \
   V(ExceptionHandlers)                                                         \
   V(Context)                                                                   \
   V(ContextScope)                                                              \
   V(UnhandledException)                                                        \
+  V(ApiFailure)                                                                \
   V(Instance)                                                                  \
     V(Number)                                                                  \
       V(Integer)                                                               \
         V(Smi)                                                                 \
         V(Mint)                                                                \
         V(Bigint)                                                              \
       V(Double)                                                                \
     V(String)                                                                  \
       V(OneByteString)                                                         \
       V(TwoByteString)                                                         \
@@ skipping 532 matching lines @@
     return reinterpret_cast<RawObject**>(&ptr()->exception_);
   }
   RawInstance* exception_;
   RawInstance* stacktrace_;
   RawObject** to() {
     return reinterpret_cast<RawObject**>(&ptr()->stacktrace_);
   }
 };
 
 
+class RawApiFailure : public RawObject {
+  RAW_HEAP_OBJECT_IMPLEMENTATION(ApiFailure);
+
+  RawObject** from() {
+    return reinterpret_cast<RawObject**>(&ptr()->message_);
+  }
+  RawString* message_;
+  RawObject** to() {
+    return reinterpret_cast<RawObject**>(&ptr()->message_);
+  }
+};
+
+
 class RawInstance : public RawObject {
   RAW_HEAP_OBJECT_IMPLEMENTATION(Instance);
 };
 
 
 class RawNumber : public RawInstance {
   RAW_OBJECT_IMPLEMENTATION(Number);
 };
 
 
@@ skipping 152 matching lines @@
   intptr_t type_;  // Uninitialized, simple or complex.
   intptr_t flags_;  // Represents global/local, case insensitive, multiline.
 
   // Variable length data follows here.
   uint8_t data_[0];
 };
 
 }  // namespace dart
 
 #endif  // VM_RAW_OBJECT_H_