[clangd] Partition include graph on auto-index.

Summary:
Partitions include graphs in auto-index so that each shards contains
only part of the include graph related to itself.

Reviewers: ilya-biryukov

Subscribers: ioeric, MaskRay, jkorous, arphaman, cfe-commits

Differential Revision: https://reviews.llvm.org/D55062

llvm-svn: 348252
diff --git a/clang-tools-extra/clangd/Headers.h b/clang-tools-extra/clangd/Headers.h
index 6757c90..f67b5c6 100644
--- a/clang-tools-extra/clangd/Headers.h
+++ b/clang-tools-extra/clangd/Headers.h
@@ -53,9 +53,9 @@
 // self-contained).
 struct IncludeGraphNode {
   // True if current file is a main file rather than a header.
-  bool IsTU;
+  bool IsTU = false;
   llvm::StringRef URI;
-  FileDigest Digest;
+  FileDigest Digest{0};
   std::vector<llvm::StringRef> DirectIncludes;
 };
 // FileURI and FileInclusions are references to keys of the map containing