Twinify GraphWriter a little bit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@144647 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/EdgeBundles.cpp b/lib/CodeGen/EdgeBundles.cpp
index a7aba89..3bb0465 100644
--- a/lib/CodeGen/EdgeBundles.cpp
+++ b/lib/CodeGen/EdgeBundles.cpp
@@ -77,7 +77,7 @@
 /// Specialize WriteGraph, the standard implementation won't work.
 raw_ostream &llvm::WriteGraph(raw_ostream &O, const EdgeBundles &G,
                               bool ShortNames,
-                              const std::string &Title) {
+                              const Twine &Title) {
   const MachineFunction *MF = G.getMachineFunction();
 
   O << "digraph {\n";