Add missing debugger root visiting.

Bug: 13634574
Change-Id: I2a76f6c43f1d0ad1922f06deb40a71ff651129fd
diff --git a/runtime/thread.cc b/runtime/thread.cc
index 8e14924..38e4204 100644
--- a/runtime/thread.cc
+++ b/runtime/thread.cc
@@ -2025,6 +2025,12 @@
   jni_env_->locals.VisitRoots(visitor, arg, thread_id, kRootJNILocal);
   jni_env_->monitors.VisitRoots(visitor, arg, thread_id, kRootJNIMonitor);
   SirtVisitRoots(visitor, arg, thread_id);
+  if (debug_invoke_req_ != nullptr) {
+    debug_invoke_req_->VisitRoots(visitor, arg, thread_id, kRootDebugger);
+  }
+  if (single_step_control_ != nullptr) {
+    single_step_control_->VisitRoots(visitor, arg, thread_id, kRootDebugger);
+  }
   // Visit roots on this thread's stack
   Context* context = GetLongJumpContext();
   RootCallbackVisitor visitorToCallback(visitor, arg, thread_id);