Do not try to patch type objects that are already canonical.

runtime/vm/object.cc

 // 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.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 15588 matching lines @@
   // Fast canonical lookup/registry for simple types.
   if ((cls.NumTypeArguments() == 0) && !cls.IsSignatureClass()) {
     type = cls.CanonicalType();
     if (type.IsNull()) {
       ASSERT(!cls.raw()->IsVMHeapObject() || (isolate == Dart::vm_isolate()));
       cls.set_canonical_types(*this);
       SetCanonical();
       return this->raw();
     }
     ASSERT(this->Equals(type));
+    ASSERT(type.IsCanonical());
     return type.raw();
   }
 
   Array& canonical_types = Array::Handle(isolate);
   canonical_types ^= cls.canonical_types();
   if (canonical_types.IsNull()) {
     canonical_types = empty_array().raw();
   }
   intptr_t length = canonical_types.Length();
   // Linear search to see whether this type is already present in the
   // list of canonicalized types.
   // TODO(asiva): Try to re-factor this lookup code to make sharing
   // easy between the 4 versions of this loop.
   intptr_t index = 0;
   while (index < length) {
     type ^= canonical_types.At(index);
     if (type.IsNull()) {
       break;
     }
     ASSERT(type.IsFinalized());
     if (this->Equals(type)) {
+      ASSERT(type.IsCanonical());
       return type.raw();
     }
     index++;
   }
   // The type was not found in the table. It is not canonical yet.
 
   // Canonicalize the type arguments.
   TypeArguments& type_args = TypeArguments::Handle(isolate, arguments());
   // In case the type is first canonicalized at runtime, its type argument
   // vector may be longer than necessary. This is not an issue.
   ASSERT(type_args.IsNull() || (type_args.Length() >= cls.NumTypeArguments()));
   type_args = type_args.Canonicalize(trail);
   set_arguments(type_args);
 
   // Canonicalizing the type arguments may have changed the index, may have
   // grown the table, or may even have canonicalized this type.
   canonical_types ^= cls.canonical_types();
   if (canonical_types.IsNull()) {
     canonical_types = empty_array().raw();
   }
   length = canonical_types.Length();
   while (index < length) {
     type ^= canonical_types.At(index);
     if (type.IsNull()) {
       break;
     }
     ASSERT(type.IsFinalized());
     if (this->Equals(type)) {
+      ASSERT(type.IsCanonical());
       return type.raw();
     }
     index++;
   }
 
   // The type needs to be added to the list. Grow the list if it is full.
   if (index == length) {
     const intptr_t new_length = (length > 64) ?
         (length + 64) :
         ((length == 0) ? 1 : (length * 2));
@@ skipping 5695 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Instance::PrintJSONImpl(stream, ref);
 }
 
 
 }  // namespace dart