split dom frontier handling stuff out to its own DominanceFrontier header,
so that Dominators.h is *just* domtree.  Also prune #includes a bit.

llvm-svn: 122714
diff --git a/llvm/lib/Transforms/Utils/BreakCriticalEdges.cpp b/llvm/lib/Transforms/Utils/BreakCriticalEdges.cpp
index 67c0494..603d598 100644
--- a/llvm/lib/Transforms/Utils/BreakCriticalEdges.cpp
+++ b/llvm/lib/Transforms/Utils/BreakCriticalEdges.cpp
@@ -19,7 +19,7 @@
 #define DEBUG_TYPE "break-crit-edges"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
-#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/DominanceFrontier.h"
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/ProfileInfo.h"
 #include "llvm/Function.h"