diff --git a/clang/lib/Frontend/TestModuleFileExtension.h b/clang/lib/Frontend/TestModuleFileExtension.h
new file mode 100644
index 0000000..2a72454
--- /dev/null
+++ b/clang/lib/Frontend/TestModuleFileExtension.h
@@ -0,0 +1,71 @@
+//===-- TestModuleFileExtension.h - Module Extension Tester -----*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_CLANG_FRONTEND_TESTMODULEFILEEXTENSION_H
+#define LLVM_CLANG_FRONTEND_TESTMODULEFILEEXTENSION_H
+
+#include "clang/Serialization/ModuleFileExtension.h"
+#include "clang/Basic/LLVM.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Bitcode/BitstreamReader.h"
+#include <string>
+
+namespace clang {
+
+/// A module file extension used for testing purposes.
+class TestModuleFileExtension : public ModuleFileExtension {
+  std::string BlockName;
+  unsigned MajorVersion;
+  unsigned MinorVersion;
+  bool Hashed;
+  std::string UserInfo;
+
+  class Writer : public ModuleFileExtensionWriter {
+  public:
+    Writer(ModuleFileExtension *Ext) : ModuleFileExtensionWriter(Ext) { }
+    ~Writer() override;
+
+    void writeExtensionContents(llvm::BitstreamWriter &Stream) override;
+  };
+
+  class Reader : public ModuleFileExtensionReader {
+    llvm::BitstreamCursor Stream;
+
+  public:
+    ~Reader() override;
+
+    Reader(ModuleFileExtension *Ext, const llvm::BitstreamCursor &InStream);
+  };
+
+public:
+  TestModuleFileExtension(StringRef BlockName,
+                          unsigned MajorVersion,
+                          unsigned MinorVersion,
+                          bool Hashed,
+                          StringRef UserInfo)
+    : BlockName(BlockName),
+      MajorVersion(MajorVersion), MinorVersion(MinorVersion),
+      Hashed(Hashed), UserInfo(UserInfo) { }
+  ~TestModuleFileExtension() override;
+
+  ModuleFileExtensionMetadata getExtensionMetadata() const override;
+
+  llvm::hash_code hashExtension(llvm::hash_code Code) const override;
+
+  std::unique_ptr<ModuleFileExtensionWriter>
+  createExtensionWriter(ASTWriter &Writer) override;
+
+  std::unique_ptr<ModuleFileExtensionReader>
+  createExtensionReader(const ModuleFileExtensionMetadata &Metadata,
+                        ASTReader &Reader, serialization::ModuleFile &Mod,
+                        const llvm::BitstreamCursor &Stream) override;
+};
+
+} // end namespace clang
+
+#endif // LLVM_CLANG_FRONTEND_TESTMODULEFILEEXTENSION_H