Make stack visitor location for bad roots more verbose.

Change-Id: Ib2f3f48ccf1f5b2f3a4d1a61df553ad1a5c29d38
diff --git a/src/gc/mark_sweep.h b/src/gc/mark_sweep.h
index 98445d4..0fee24f 100644
--- a/src/gc/mark_sweep.h
+++ b/src/gc/mark_sweep.h
@@ -295,9 +295,9 @@
   void ExpandMarkStack();
 
   static void VerifyRootCallback(const Object* root, void* arg, size_t vreg,
-                                 const AbstractMethod* method);
+                                 const StackVisitor *visitor);
 
-  void VerifyRoot(const Object* root, size_t vreg, const AbstractMethod* method)
+  void VerifyRoot(const Object* root, size_t vreg, const StackVisitor* visitor)
       NO_THREAD_SAFETY_ANALYSIS;
 
   template <typename Visitor>