Add missing #include found by modules buildbot.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@230532 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Sema/CodeCompleteConsumer.h

@@ -17,6 +17,7 @@
 #include "clang/AST/CanonicalType.h"
 #include "clang/AST/Type.h"
 #include "clang/Sema/CodeCompleteOptions.h"
+#include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Allocator.h"