Clean up AtomicDexRefMap

Make ClassReference, TypeReference, and MethodReference extend
DexFileReference. This enables using all of these types as the key
for AtomicDexRefMap.

Test: test-art-host
Bug: 63851220
Bug: 63756964

Change-Id: Ida3c94cadb53272cb5057e5cebc5971c1ab4d366
diff --git a/runtime/dex_file_reference.h b/runtime/dex_file_reference.h
new file mode 100644
index 0000000..01a6425
--- /dev/null
+++ b/runtime/dex_file_reference.h
@@ -0,0 +1,52 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef ART_RUNTIME_DEX_FILE_REFERENCE_H_
+#define ART_RUNTIME_DEX_FILE_REFERENCE_H_
+
+#include <cstdint>
+
+namespace art {
+
+class DexFile;
+
+class DexFileReference {
+ public:
+  DexFileReference(const DexFile* file, uint32_t idx) : dex_file(file), index(idx) {}
+  const DexFile* dex_file;
+  uint32_t index;
+
+  struct Comparator {
+    bool operator()(const DexFileReference& a, const DexFileReference& b) const {
+      if (a.dex_file != b.dex_file) {
+        return a.dex_file < b.dex_file;
+      }
+      return a.index < b.index;
+    }
+  };
+};
+
+// Default comparators, compares the indicies, not the backing data.
+inline bool operator<(const DexFileReference& a, const DexFileReference& b) {
+  return DexFileReference::Comparator()(a, b);
+}
+inline bool operator==(const DexFileReference& a, const DexFileReference& b) {
+  return a.dex_file == b.dex_file && a.index == b.index;
+}
+
+}  // namespace art
+
+#endif  // ART_RUNTIME_DEX_FILE_REFERENCE_H_