[base] Implement Windows::Foundation::IReference

This change provides an implementation of Windows::Foundation's
IReference interface. This class is supposed to be used for optional
POD types, as a null value usually is not possible here.

Bug: 821766
Change-Id: Icc6ff4f5313e2cfa13ca33f8d54e150efa616d76
Reviewed-on: https://chromium-review.googlesource.com/1106385Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Robert Liao <robliao@chromium.org>
Commit-Queue: Jan Wilken Dörrie <jdoerrie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568877}

base/BUILD.gn

@@ -1052,6 +1052,7 @@ jumbo_component("base") {
     "win/patch_util.h",
     "win/process_startup_helper.cc",
     "win/process_startup_helper.h",
+    "win/reference.h",
     "win/registry.cc",
     "win/registry.h",
     "win/resource_util.cc",
@@ -2443,6 +2444,7 @@ test("base_unittests") {
     "win/message_window_unittest.cc",
     "win/object_watcher_unittest.cc",
     "win/pe_image_unittest.cc",
+    "win/reference_unittest.cc",
     "win/registry_unittest.cc",
     "win/scoped_bstr_unittest.cc",
     "win/scoped_handle_unittest.cc",

base/win/reference.h

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_WIN_REFERENCE_H_
+#define BASE_WIN_REFERENCE_H_
+
+#include <windows.foundation.collections.h>
+#include <wrl/implements.h>
+
+#include <type_traits>
+#include <utility>
+
+#include "base/macros.h"
+
+namespace base {
+namespace win {
+
+// Implementation of the UWP's IReference interface.
+template <typename T>
+class Reference
+    : public Microsoft::WRL::RuntimeClass<
+          Microsoft::WRL::RuntimeClassFlags<
+              Microsoft::WRL::WinRt | Microsoft::WRL::InhibitRoOriginateError>,
+          ABI::Windows::Foundation::IReference<T>> {
+ public:
+  using AbiT = typename ABI::Windows::Foundation::Internal::GetAbiType<
+      typename ABI::Windows::Foundation::IReference<T>::T_complex>::type;
+
+  explicit Reference(const AbiT& value) : value_(value) {}
+  explicit Reference(AbiT&& value) : value_(std::move(value)) {}
+
+  // ABI::Windows::Foundation::IReference:
+  IFACEMETHODIMP get_Value(AbiT* value) override {
+    *value = value_;
+    return S_OK;
+  }
+
+ private:
+  ~Reference() = default;
+  AbiT value_;
+
+  DISALLOW_COPY_AND_ASSIGN(Reference);
+};
+
+}  // namespace win
+}  // namespace base
+
+#endif  // BASE_WIN_REFERENCE_H_

base/win/reference_unittest.cc

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/win/reference.h"
+
+#include <windows.foundation.h>
+#include <wrl/client.h>
+
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace base {
+namespace win {
+
+namespace {
+
+using Microsoft::WRL::Make;
+
+}  // namespace
+
+TEST(ReferenceTest, Value) {
+  auto ref = Make<Reference<int>>(123);
+  int value = 0;
+  HRESULT hr = ref->get_Value(&value);
+  EXPECT_TRUE(SUCCEEDED(hr));
+  EXPECT_EQ(123, value);
+}
+
+TEST(ReferenceTest, ValueAggregate) {
+  auto ref = Make<Reference<bool>>(true);
+  boolean value = false;
+  HRESULT hr = ref->get_Value(&value);
+  EXPECT_TRUE(SUCCEEDED(hr));
+  EXPECT_TRUE(value);
+}
+
+}  // namespace win
+}  // namespace base