[clangd] Inactive regions support as an extension to semantic highlighting

Differential Revision: https://reviews.llvm.org/D67536
diff --git a/clang-tools-extra/clangd/Protocol.cpp b/clang-tools-extra/clangd/Protocol.cpp
index bdf284d..25826bd 100644
--- a/clang-tools-extra/clangd/Protocol.cpp
+++ b/clang-tools-extra/clangd/Protocol.cpp
@@ -1063,7 +1063,8 @@
 
 llvm::json::Value toJSON(const SemanticHighlightingInformation &Highlighting) {
   return llvm::json::Object{{"line", Highlighting.Line},
-                            {"tokens", Highlighting.Tokens}};
+                            {"tokens", Highlighting.Tokens},
+                            {"isInactive", Highlighting.IsInactive}};
 }
 
 llvm::json::Value toJSON(const SemanticHighlightingParams &Highlighting) {