Replace OwningPtr with std::unique_ptr.

This compiles cleanly with lldb/lld/clang-tools-extra/llvm.

llvm-svn: 203279
diff --git a/clang/lib/Basic/FileManager.cpp b/clang/lib/Basic/FileManager.cpp
index 4431e45..579c818 100644
--- a/clang/lib/Basic/FileManager.cpp
+++ b/clang/lib/Basic/FileManager.cpp
@@ -379,7 +379,7 @@
 llvm::MemoryBuffer *FileManager::
 getBufferForFile(const FileEntry *Entry, std::string *ErrorStr,
                  bool isVolatile) {
-  OwningPtr<llvm::MemoryBuffer> Result;
+  std::unique_ptr<llvm::MemoryBuffer> Result;
   llvm::error_code ec;
 
   uint64_t FileSize = Entry->getSize();
@@ -417,7 +417,7 @@
 
 llvm::MemoryBuffer *FileManager::
 getBufferForFile(StringRef Filename, std::string *ErrorStr) {
-  OwningPtr<llvm::MemoryBuffer> Result;
+  std::unique_ptr<llvm::MemoryBuffer> Result;
   llvm::error_code ec;
   if (FileSystemOpts.WorkingDir.empty()) {
     ec = FS->getBufferForFile(Filename, Result);