Add base::FeatureParam<> struct

base/metrics/field_trial_params_unittest.nc

+// Copyright 2017 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.
+
+// This is a "No Compile Test" suite.
+// http://dev.chromium.org/developers/testing/no-compile-tests
+
+#include "base/metrics/field_trial_params.h"
+
+constexpr base::Feature kFeature{"NoCompileFeature"};
+
+enum Param { FOO, BAR };
+
+#if defined(NCTEST_NO_PARAM_TYPE)
+
+constexpr base::FieldParam<> kParam{  // ["need error string"]
+  &kFeature, "Param"};
+
+#elif defined(NCTEST_VOID_PARAM_TYPE)
+
+constexpr base::FieldParam<> kParam{  // ["need error string"]
+  &kFeature, "Param"};
+
+#elif defined(NCTEST_INVALID_PARAM_TYPE)
+
+constexpr base::FieldParam<unsigned> kParam{  // ["need error string"]
+  &kFeature, "Param", 1u};
+
+#elif defined(NCTEST_ENUM_NULL_OPTIONS)
+
+constexpr base::FieldParam<Param> kParam{  // ["need error string"]
+  &kFeature, "Param", FOO, nullptr};
+
+#elif defined(NCTEST_ENUM_EMPTY_OPTIONS)
+
+constexpr base::FieldParam<Param>::Option[] kParamOptions = {};
+constexpr base::FieldParam<Param> kParam{
+  &kFeature, "Param", FOO, &kParamOptions};
+
+#endif