ObjPtr<>-ify Monitor/-Pool.

Test: m test-art-host-gtest
Test: testrunner.py --host
Bug: 31113334
Change-Id: I2d2ebc5ef56e73e5678e0cfcd84c479611dfcca8
diff --git a/openjdkjvmti/ti_stack.cc b/openjdkjvmti/ti_stack.cc
index 5e934df..b96c92a 100644
--- a/openjdkjvmti/ti_stack.cc
+++ b/openjdkjvmti/ti_stack.cc
@@ -844,18 +844,17 @@
     return true;
   }
 
-  static void AppendOwnedMonitors(art::mirror::Object* owned_monitor, void* arg)
+  static void AppendOwnedMonitors(art::ObjPtr<art::mirror::Object> owned_monitor, void* arg)
       REQUIRES_SHARED(art::Locks::mutator_lock_) {
     art::Locks::mutator_lock_->AssertSharedHeld(art::Thread::Current());
     MonitorVisitor* visitor = reinterpret_cast<MonitorVisitor*>(arg);
-    art::ObjPtr<art::mirror::Object> mon(owned_monitor);
     // Filter out duplicates.
     for (const art::Handle<art::mirror::Object>& monitor : visitor->monitors) {
-      if (monitor.Get() == mon.Ptr()) {
+      if (monitor.Get() == owned_monitor) {
         return;
       }
     }
-    visitor->monitors.push_back(visitor->hs.NewHandle(mon));
+    visitor->monitors.push_back(visitor->hs.NewHandle(owned_monitor));
     visitor->stack_depths.push_back(visitor->current_stack_depth);
   }