[C++11] Replace OwningPtr with std::unique_ptr.

This removes all references to OwningPtr, which should be fairly
undisruptive to out-of-tree projects since they are unlikely to use
clang-tools-extra as a library instead of a set of tools.

llvm-svn: 203382
diff --git a/clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.h b/clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.h
index 76b6aaa..31173e3 100644
--- a/clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.h
+++ b/clang-tools-extra/clang-tidy/ClangTidyDiagnosticConsumer.h
@@ -128,7 +128,7 @@
   void finalizeLastError();
 
   ClangTidyContext &Context;
-  OwningPtr<DiagnosticsEngine> Diags;
+  std::unique_ptr<DiagnosticsEngine> Diags;
   SmallVector<ClangTidyError, 8> Errors;
   bool LastErrorRelatesToUserCode;
 };