Make MultiplexASTDeserializationListener part of the API [NFC]

[teemperor]

Summary

This patch moves the MultiplexASTDeserializationListener declaration into a public header.

We're currently using this multiplexer in the cling interpreter to attach another
ASTDeserializationListener during the execution (so, after the MultiplexConsumer is already
attached which prevents us from attaching more). So far we're doing this by patching clang
and making this class public, but it makes things easier if we make this instead just public in
upstream.

[bruno]

LGTM

include/clang/Frontend/MultiplexConsumer.h

 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_CLANG_FRONTEND_MULTIPLEXCONSUMER_H
 #define LLVM_CLANG_FRONTEND_MULTIPLEXCONSUMER_H
 
 #include "clang/Basic/LLVM.h"
 #include "clang/Sema/SemaConsumer.h"
+#include "clang/Serialization/ASTDeserializationListener.h"
 #include <memory>
 #include <vector>
 
 namespace clang {
 
 class MultiplexASTMutationListener;
-class MultiplexASTDeserializationListener;
+
+// This ASTDeserializationListener forwards its notifications to a set of
+// child listeners.
+class MultiplexASTDeserializationListener : public ASTDeserializationListener {
+public:
+  // Does NOT take ownership of the elements in L.
+  MultiplexASTDeserializationListener(
+      const std::vector<ASTDeserializationListener *> &L);
+  void ReaderInitialized(ASTReader *Reader) override;
+  void IdentifierRead(serialization::IdentID ID, IdentifierInfo *II) override;
+  void MacroRead(serialization::MacroID ID, MacroInfo *MI) override;
+  void TypeRead(serialization::TypeIdx Idx, QualType T) override;
+  void DeclRead(serialization::DeclID ID, const Decl *D) override;
+  void SelectorRead(serialization::SelectorID iD, Selector Sel) override;
+  void MacroDefinitionRead(serialization::PreprocessedEntityID,
+                           MacroDefinitionRecord *MD) override;
+  void ModuleRead(serialization::SubmoduleID ID, Module *Mod) override;
+
+private:
+  std::vector<ASTDeserializationListener *> Listeners;
+};
 
 // Has a list of ASTConsumers and calls each of them. Owns its children.
 class MultiplexConsumer : public SemaConsumer {
 public:
   // Takes ownership of the pointers in C.
   MultiplexConsumer(std::vector<std::unique_ptr<ASTConsumer>> C);
   ~MultiplexConsumer() override;
 

lib/Frontend/MultiplexConsumer.cpp

 //  MultiplexASTDeserializationListener and  MultiplexASTMutationListener, which
 //  are implementation details of MultiplexConsumer.
 //
 //===----------------------------------------------------------------------===//
 
 #include "clang/Frontend/MultiplexConsumer.h"
 #include "clang/AST/ASTMutationListener.h"
 #include "clang/AST/DeclGroup.h"
-#include "clang/Serialization/ASTDeserializationListener.h"
 
 using namespace clang;
 
 namespace clang {
 
-// This ASTDeserializationListener forwards its notifications to a set of
-// child listeners.
-class MultiplexASTDeserializationListener
-    : public ASTDeserializationListener {
-public:
-  // Does NOT take ownership of the elements in L.
-  MultiplexASTDeserializationListener(
-      const std::vector<ASTDeserializationListener*>& L);
-  void ReaderInitialized(ASTReader *Reader) override;
-  void IdentifierRead(serialization::IdentID ID,
-                      IdentifierInfo *II) override;
-  void MacroRead(serialization::MacroID ID, MacroInfo *MI) override;
-  void TypeRead(serialization::TypeIdx Idx, QualType T) override;
-  void DeclRead(serialization::DeclID ID, const Decl *D) override;
-  void SelectorRead(serialization::SelectorID iD, Selector Sel) override;
-  void MacroDefinitionRead(serialization::PreprocessedEntityID,
-                           MacroDefinitionRecord *MD) override;
-  void ModuleRead(serialization::SubmoduleID ID, Module *Mod) override;
-
-private:
-  std::vector<ASTDeserializationListener *> Listeners;
-};
-
 MultiplexASTDeserializationListener::MultiplexASTDeserializationListener(
       const std::vector<ASTDeserializationListener*>& L)
     : Listeners(L) {
 }
 
 void MultiplexASTDeserializationListener::ReaderInitialized(
     ASTReader *Reader) {
   for (size_t i = 0, e = Listeners.size(); i != e; ++i)