Add a verification step which iterates over the heap and verifies that all canonical objects are co…

runtime/vm/verifier.h

Index: runtime/vm/verifier.h
diff --git a/runtime/vm/verifier.h b/runtime/vm/verifier.h
index a34d7f6305ff0939bce8a3ac741c1dde6aeb5f7e..8ae222d661fcf0b3267463e2c2a35e447f09f50d 100644
--- a/runtime/vm/verifier.h
+++ b/runtime/vm/verifier.h
@@ -81,6 +81,21 @@ class VerifyWeakPointersVisitor : public HandleVisitor {
   DISALLOW_COPY_AND_ASSIGN(VerifyWeakPointersVisitor);
 };
 
+
+#if defined(DEBUG)
+class VerifyCanonicalVisitor : public ObjectVisitor {
+ public:
+  explicit VerifyCanonicalVisitor(Thread* thread);
+  virtual void VisitObject(RawObject* obj);
+
+ private:
+  Thread* thread_;
+  Instance& instanceHandle_;
+
+  DISALLOW_COPY_AND_ASSIGN(VerifyCanonicalVisitor);
+};
+#endif  // defined(DEBUG)
+
 }  // namespace dart
 
 #endif  // VM_VERIFIER_H_