add features module to detect availability of build time features at runtime

atom/common/api/features.cc

@@ -0,0 +1,28 @@
+// Copyright (c) 2018 GitHub, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#include "atom/common/node_includes.h"
+#include "native_mate/dictionary.h"
+
+namespace {
+
+bool IsPDFViewerEnabled() {
+#if defined(ENABLE_PDF_VIEWER)
+  return true;
+#else
+  return false;
+#endif
+}
+
+void Initialize(v8::Local<v8::Object> exports,
+                v8::Local<v8::Value> unused,
+                v8::Local<v8::Context> context,
+                void* priv) {
+  mate::Dictionary dict(context->GetIsolate(), exports);
+  dict.SetMethod("isPDFViewerEnabled", &IsPDFViewerEnabled);
+}
+
+}  // namespace
+
+NODE_BUILTIN_MODULE_CONTEXT_AWARE(atom_common_features, Initialize)