Ambiguous references do not necessarily cause compilation errors (issue 5736).

runtime/vm/class_finalizer.h

Index: runtime/vm/class_finalizer.h
===================================================================
--- runtime/vm/class_finalizer.h	(revision 13985)
+++ runtime/vm/class_finalizer.h	(working copy)
@@ -49,12 +49,15 @@
                                        FinalizationKind finalization);
 
   // Allocate, finalize, and return a new malformed type as if it was declared
-  // in class cls at the given token position. Build the error message from the
-  // format string and its arguments.
-  static RawType* NewFinalizedMalformedType(const Class& cls,
+  // in class cls at the given token position.
+  // If not null, prepend prev_error to the error message built from the format
+  // string and its arguments.
+  static RawType* NewFinalizedMalformedType(const Error& prev_error,
+                                            const Class& cls,
                                             intptr_t type_pos,
+                                            FinalizationKind finalization,
                                             const char* format, ...)
-       PRINTF_ATTRIBUTE(3, 4);
+       PRINTF_ATTRIBUTE(5, 6);
 
   // Depending on the given type, finalization mode, and execution mode, mark
   // the given type as malformed or report a compile time error.