[clangd] Replaced WorkerRequest with std::function...

Summary:
And implemented a helper function to dump an AST of a file for
testing/debugging purposes.

Reviewers: bkramer, krasimir

Reviewed By: krasimir

Subscribers: klimek, cfe-commits

Tags: #clang-tools-extra

Differential Revision: https://reviews.llvm.org/D33415

llvm-svn: 303634
diff --git a/clang-tools-extra/clangd/ClangdUnit.cpp b/clang-tools-extra/clangd/ClangdUnit.cpp
index 6fe90e8..fb029b7 100644
--- a/clang-tools-extra/clangd/ClangdUnit.cpp
+++ b/clang-tools-extra/clangd/ClangdUnit.cpp
@@ -222,3 +222,7 @@
   }
   return Result;
 }
+
+void ClangdUnit::dumpAST(llvm::raw_ostream &OS) const {
+  Unit->getASTContext().getTranslationUnitDecl()->dump(OS, true);
+}