Add Dart_PropagateError.

runtime/vm/exceptions.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_EXCEPTIONS_H_
 #define VM_EXCEPTIONS_H_
 
 #include "vm/allocation.h"
 #include "vm/growable_array.h"
 
 namespace dart {
 
 // Forward declarations.
+class Error;
 class Instance;
 class Object;
-class RawInstance;
+class RawObject;
 
 class Exceptions : AllStatic {
  public:
   static void Throw(const Instance& exception);
   static void ReThrow(const Instance& exception, const Instance& stacktrace);
+  static void PropagateError(const Object& obj);
 
   enum ExceptionType {
     kIndexOutOfRange,
     kIllegalArgument,
     kNoSuchMethod,
     kClosureArgumentMismatch,
     kObjectNotClosure,
     kBadNumberFormat,
     kStackOverflow,
     kOutOfMemory,
     kWrongArgumentCount,
     kInternalError,
     kNullPointer,
     kIllegalJSRegExp,
   };
 
   static void ThrowByType(ExceptionType type,
                           const GrowableArray<const Object*>& arguments);
-  static RawInstance* Create(ExceptionType type,
-                             const GrowableArray<const Object*>& arguments);
+  // Returns a RawInstance if the exception is successfully created,
+  // otherwise returns a RawError.
+  static RawObject* Create(ExceptionType type,
+                           const GrowableArray<const Object*>& arguments);
 
  private:
   DISALLOW_COPY_AND_ASSIGN(Exceptions);
 };
 
 }  // namespace dart
 
 #endif  // VM_EXCEPTIONS_H_