Fix CC root visiting bug

Also some cleanup.

Change-Id: Ia3de8f2d409770be3619ec116e8b06ecd82338fe
diff --git a/runtime/indirect_reference_table.cc b/runtime/indirect_reference_table.cc
index a3aa1de..cd59365 100644
--- a/runtime/indirect_reference_table.cc
+++ b/runtime/indirect_reference_table.cc
@@ -243,7 +243,7 @@
 }
 
 void IndirectReferenceTable::VisitRoots(RootVisitor* visitor, const RootInfo& root_info) {
-  BufferedRootVisitor<128> root_visitor(visitor, root_info);
+  BufferedRootVisitor<kDefaultBufferedRootCount> root_visitor(visitor, root_info);
   for (auto ref : *this) {
     root_visitor.VisitRootIfNonNull(*ref);
   }