Add DCHECKS for class-defs only being null for Proxy classes

Follow-up to go/aog/518436

Test: ./test.py --host -j50
Bug: 68157595
Change-Id: I4e56d7454caef2023bd367841fb9a57fbecda748
diff --git a/runtime/dex_file_annotations.cc b/runtime/dex_file_annotations.cc
index 6075230..845202f 100644
--- a/runtime/dex_file_annotations.cc
+++ b/runtime/dex_file_annotations.cc
@@ -136,6 +136,7 @@
   ObjPtr<mirror::Class> klass = field->GetDeclaringClass();
   const DexFile::ClassDef* class_def = klass->GetClassDef();
   if (class_def == nullptr) {
+    DCHECK(klass->IsProxyClass());
     return nullptr;
   }
   const DexFile::AnnotationsDirectoryItem* annotations_dir =
@@ -314,6 +315,7 @@
   const DexFile& dex_file = klass.GetDexFile();
   const DexFile::ClassDef* class_def = klass.GetClassDef();
   if (class_def == nullptr) {
+    DCHECK(klass.GetRealClass()->IsProxyClass());
     return nullptr;
   }
   const DexFile::AnnotationsDirectoryItem* annotations_dir =