Revert "Revert "Revert "Revert "Add intrinsic for Reference.get()""""

Fixed TargetReg issue causing build failure for x86.
This reverts commit 9e82bd3f0ce9e5f5777bea2f752ff3e251d32f9f.

Change-Id: I7e6a526954467aaf68deeed999880dfe9aa5f06e
diff --git a/runtime/runtime.cc b/runtime/runtime.cc
index c354ad5..70820eb 100644
--- a/runtime/runtime.cc
+++ b/runtime/runtime.cc
@@ -925,6 +925,7 @@
   mirror::ArtField::VisitRoots(callback, arg);
   mirror::ArtMethod::VisitRoots(callback, arg);
   mirror::Class::VisitRoots(callback, arg);
+  mirror::Reference::VisitRoots(callback, arg);
   mirror::StackTraceElement::VisitRoots(callback, arg);
   mirror::String::VisitRoots(callback, arg);
   mirror::Throwable::VisitRoots(callback, arg);