Added "PreprocessorFactory", an interface for lazily creating Preprocessor objects on-demand.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@49868 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Lex/Preprocessor.h

@@ -524,6 +524,14 @@ public:
   void HandlePragmaDependency(Token &DependencyTok);
 };
 
+/// PreprocessorFactory - A generic factory interface for lazily creating
+///  Preprocessor objects on-demand when they are needed.
+class PreprocessorFactory {
+public:
+  virtual ~PreprocessorFactory();
+  virtual Preprocessor* CreatePreprocessor() = 0;  
+};
+  
 }  // end namespace clang
 
 #endif

lib/Lex/Preprocessor.cpp

@@ -40,6 +40,8 @@ using namespace clang;
 
 //===----------------------------------------------------------------------===//
 
+PreprocessorFactory::~PreprocessorFactory() {}
+
 Preprocessor::Preprocessor(Diagnostic &diags, const LangOptions &opts,
                            TargetInfo &target, SourceManager &SM, 
                            HeaderSearch &Headers)