Start implementing jdb "locals".

This lets us show the names and types of the locals, but all the values
will show up as 0/null. We're going to have to walk the whole stack and
take callee-save frames into account to do that right.

Change-Id: Ic6e115513b6e65ae7ed4b7274e70bc514e83190a
diff --git a/src/class_linker.cc b/src/class_linker.cc
index 3e547e4..c214b5f 100644
--- a/src/class_linker.cc
+++ b/src/class_linker.cc
@@ -781,7 +781,7 @@
   DCHECK(arg != NULL);
   ClassLinker* class_linker = reinterpret_cast<ClassLinker*>(arg);
 
-  if (obj->IsString()) {
+  if (obj->GetClass()->IsStringClass()) {
     class_linker->intern_table_->RegisterStrong(obj->AsString());
     return;
   }