Make the "sticky error" an Error instead of a String.

runtime/vm/class_finalizer.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_CLASS_FINALIZER_H_
 #define VM_CLASS_FINALIZER_H_
 
 #include "vm/allocation.h"
 #include "vm/growable_array.h"
 
 namespace dart {
 
 class AbstractType;
 class AbstractTypeArguments;
 class Class;
+class Error;
 class Function;
 class RawAbstractType;
 class RawClass;
 class RawType;
 class Script;
-class String;
 class Type;
 class UnresolvedClass;
 
 // Traverses all pending, unfinalized classes, validates and marks them as
 // finalized.
 class ClassFinalizer : public AllStatic {
  public:
   enum {
     kGeneratingSnapshot = true,
     kNotGeneratingSnapshot = false
   };
 
   // Add 'interface' to 'interface_list' if it is not already in the list and
   // return true. Also return true if 'interface' is not added, because it is
   // not unique, i.e. it is already in the list.
   // Return false if 'interface' conflicts with an interface already in the list
   // with the same class, but different type arguments.
   // In the case of a conflict, set 'conflicting' to the existing interface.
   static bool AddInterfaceIfUnique(GrowableArray<AbstractType*>* interface_list,
                                    AbstractType* interface,
                                    AbstractType* conflicting);
 
   // Finalize and canonicalize type while parsing class cls.
-  // Set the error message on failure (to String::null() if no error).
+  // Set the error message on failure (to Error::null() if no error).
   static RawAbstractType* FinalizeAndCanonicalizeType(const Class& cls,
                                                       const AbstractType& type,
-                                                      String* errmsg);
+                                                      Error* error);
 
   // Pending classes are classes that need to be finalized.
   static void AddPendingClasses(const GrowableArray<const Class*>& classes);
 
   // Return false if we still have classes pending to be finalized.
   static bool AllClassesFinalized();
 
   // Return whether class finalization failed.
   // The function returns true if the finalization was successful.
   // If finalization fails, an error message is set in the sticky error field
@@ skipping 40 matching lines @@
                           const char* format, ...);
   static void ReportError(const char* format, ...);
   static void ReportWarning(const Script& script,
                             intptr_t token_index,
                             const char* format, ...);
 };
 
 }  // namespace dart
 
 #endif  // VM_CLASS_FINALIZER_H_