Make stack visitor location for bad roots more verbose.

Change-Id: Ib2f3f48ccf1f5b2f3a4d1a61df553ad1a5c29d38
diff --git a/src/heap.h b/src/heap.h
index 22b009c..67d8c05 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -53,6 +53,7 @@
 class Object;
 class Space;
 class SpaceTest;
+class StackVisitor;
 class Thread;
 class TimingLogger;
 
@@ -107,7 +108,7 @@
 
   typedef void (RootVisitor)(const Object* root, void* arg);
   typedef void (VerifyRootVisitor)(const Object* root, void* arg, size_t vreg,
-      const AbstractMethod* method);
+      const StackVisitor* visitor);
   typedef bool (IsMarkedTester)(const Object* object, void* arg);
 
   // Create a heap with the requested sizes. The possible empty