Move a method from IdentifierTable.h out of line and remove the SmallString include.

Fix all the transitive include users.

llvm-svn: 149783
diff --git a/clang/lib/AST/DumpXML.cpp b/clang/lib/AST/DumpXML.cpp
index c5e23cc..3ce02b0 100644
--- a/clang/lib/AST/DumpXML.cpp
+++ b/clang/lib/AST/DumpXML.cpp
@@ -39,8 +39,7 @@
 #include "clang/AST/TypeVisitor.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/ExprCXX.h"
-#include "llvm/ADT/SmallVector.h"
-#include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/SmallString.h"
 
 using namespace clang;