[NFC] Added DominanceInfo::dump.

Just call to the superclass' print method.

Author: nate-chandler

include/swift/SIL/Dominance.h

@@ -86,6 +86,10 @@ class DominanceInfo : public DominatorTreeBase {
   void reset() {
     super::reset();
   }
+
+#ifndef NDEBUG
+  void dump() { print(llvm::errs()); };
+#endif
 };
 
 /// Compute a single block's dominance frontier.