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/mirror/string.cc b/runtime/mirror/string.cc
index 10ae066..6f4ead9 100644
--- a/runtime/mirror/string.cc
+++ b/runtime/mirror/string.cc
@@ -280,9 +280,9 @@
   return countDiff;
 }
 
-void String::VisitRoots(RootVisitor* visitor, void* arg) {
+void String::VisitRoots(RootCallback* callback, void* arg) {
   if (java_lang_String_ != nullptr) {
-    java_lang_String_ = down_cast<Class*>(visitor(java_lang_String_, arg));
+    java_lang_String_ = down_cast<Class*>(callback(java_lang_String_, arg, 0, kRootStickyClass));
   }
 }