ObjPtr<>-ify annotation processing.

Test: Rely on TreeHugger.
Bug: 31113334
Change-Id: Ifd69c15c0df1530d8860cf50e06bde0d356b0c23
diff --git a/runtime/interpreter/unstarted_runtime.cc b/runtime/interpreter/unstarted_runtime.cc
index 791ebf0..0e429a6 100644
--- a/runtime/interpreter/unstarted_runtime.cc
+++ b/runtime/interpreter/unstarted_runtime.cc
@@ -510,7 +510,7 @@
     result->SetZ(false);
     return;
   }
-  mirror::String* class_name = nullptr;
+  ObjPtr<mirror::String> class_name = nullptr;
   if (!annotations::GetInnerClass(klass, &class_name)) {
     result->SetZ(false);
     return;