Minor cleanup to the code-completion-point logic suggested by Chris.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@90459 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Lex/Preprocessor.cpp b/lib/Lex/Preprocessor.cpp
index c757820..229826a 100644
--- a/lib/Lex/Preprocessor.cpp
+++ b/lib/Lex/Preprocessor.cpp
@@ -240,7 +240,7 @@
   return false;
 }
 
-bool Preprocessor::isCodeCompletionFile(SourceLocation FileLoc) {
+bool Preprocessor::isCodeCompletionFile(SourceLocation FileLoc) const {
   return CodeCompletionFile && FileLoc.isFileID() &&
     SourceMgr.getFileEntryForID(SourceMgr.getFileID(FileLoc))
       == CodeCompletionFile;