Cherry pick 18.4 changes to udc-widevine-dev

Get the udc-widevine-dev Android branch and oemcrypto-v18 cdm branch in
sync. The commit ID for 18.4 on oemcrypto-v18 is
a2f23a2281e5e06dc2867585bdc516fa132b6396.

Merged from go/wvgerrit/190151

Bug: 290252845
Test: WVTS tests are running and passing
Change-Id: I457332e7ca70a5b5169345e1279b3eb9f18413b6

libwvdrmengine/cdm/test/level3_file_system_ce_test.h

@@ -0,0 +1,33 @@
+// Copyright 2018 Google LLC. All Rights Reserved. This file and proprietary
+// source code may only be used and distributed under the Widevine License
+// Agreement.
+
+/*********************************************************************
+ * level3_file_system_ce_test.h
+ *
+ * Test file system for CE CDM for OEMCrypto Level3 File Operations.
+ *********************************************************************/
+
+#ifndef LEVEL3_FILE_SYSTEM_CE_TEST_H_
+#define LEVEL3_FILE_SYSTEM_CE_TEST_H_
+
+#include "cdm.h"
+#include "file_store.h"
+#include "level3_file_system.h"
+
+namespace wvoec3 {
+
+class OEMCrypto_Level3CETestFileSystem : public OEMCrypto_Level3FileSystem {
+ public:
+  OEMCrypto_Level3CETestFileSystem() {}
+  ~OEMCrypto_Level3CETestFileSystem() override {}
+  ssize_t Read(const char* filename, void* buffer, size_t size) override;
+  ssize_t Write(const char* filename, const void* buffer, size_t size) override;
+  bool Exists(const char* filename) override;
+  ssize_t FileSize(const char* filename) override;
+  bool Remove(const char* filename) override;
+};
+
+}  // namespace wvoec3
+
+#endif