[turbofan] small cleanups to aid register allocator debugging

src/compiler/register-allocator.h

Index: src/compiler/register-allocator.h
diff --git a/src/compiler/register-allocator.h b/src/compiler/register-allocator.h
index a6578af7ecb727894f7e290f1cbbc2c28e8d1460..067ed871c43b7c64cade3616518ea8bc9787d56e 100644
--- a/src/compiler/register-allocator.h
+++ b/src/compiler/register-allocator.h
@@ -388,6 +388,7 @@ class RegisterAllocator FINAL {
   bool IsOutputRegisterOf(Instruction* instr, int index);
   bool IsOutputDoubleRegisterOf(Instruction* instr, int index);
   void ProcessInstructions(const InstructionBlock* block, BitVector* live);
+  bool ExistsUseWithoutDefinition();
   void MeetRegisterConstraints(const InstructionBlock* block);
   void MeetConstraintsBetween(Instruction* first, Instruction* second,
                               int gap_index);