Mark breakpoint roots

Used to prevent class unloading on methods that have breakpoints.

Bug: 22720414
Change-Id: I9aee8bcbfdf253607e89dfc55a50ba3f11d99206
diff --git a/runtime/runtime.cc b/runtime/runtime.cc
index 1f447d0..9fb21a8 100644
--- a/runtime/runtime.cc
+++ b/runtime/runtime.cc
@@ -1426,6 +1426,7 @@
     // Guaranteed to have no new roots in the constant roots.
     VisitConstantRoots(visitor);
   }
+  Dbg::VisitRoots(visitor);
 }
 
 void Runtime::VisitTransactionRoots(RootVisitor* visitor) {