Add root types and thread id to root visiting.

Enables us to pass the root type and thread id to hprof.

Bug: 12680863
Change-Id: I6a0f1f9e3aa8f9b4033d695818ae7ca3460d67cb
diff --git a/runtime/gc/space/bump_pointer_space.cc b/runtime/gc/space/bump_pointer_space.cc
index a314d74..2e07bd3 100644
--- a/runtime/gc/space/bump_pointer_space.cc
+++ b/runtime/gc/space/bump_pointer_space.cc
@@ -137,7 +137,7 @@
   return storage;
 }
 
-void BumpPointerSpace::Walk(ObjectVisitorCallback callback, void* arg) {
+void BumpPointerSpace::Walk(ObjectCallback* callback, void* arg) {
   byte* pos = Begin();
 
   {