Move mirror::ObjectArray to ObjPtr

Also reduce calls to ObjPtr::Ptr.

Bug: 31113334

Test: test-art-host -j32

Change-Id: I73e1b356972bb079b66332f00f7f07451601044e
diff --git a/runtime/mirror/array.cc b/runtime/mirror/array.cc
index aee48cc..1aa38dd 100644
--- a/runtime/mirror/array.cc
+++ b/runtime/mirror/array.cc
@@ -121,7 +121,7 @@
   art::ThrowArrayIndexOutOfBoundsException(index, GetLength());
 }
 
-void Array::ThrowArrayStoreException(Object* object) {
+void Array::ThrowArrayStoreException(ObjPtr<Object> object) {
   art::ThrowArrayStoreException(object->GetClass(), this->GetClass());
 }