Make IsDeadlockDetect() virtual member of Transaction

Summary: Make `IsDeadlockDetect()` virtual member of base class `Transaction` for ease of use in MyRocks

Test Plan: compiles. compiles into MyRocks call-site.

Reviewers: mung

Reviewed By: mung

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D65385

include/rocksdb/utilities/transaction.h

@@ -399,6 +399,8 @@ class Transaction {
 
   virtual TransactionID GetID() const { return 0; }
 
+  virtual bool IsDeadlockDetect() const { return false; }
+
   virtual TransactionID GetWaitingTxn(uint32_t* column_family_id,
                                       const std::string** key) const {
     assert(false);

utilities/transactions/transaction_impl.h

@@ -91,7 +91,7 @@ class TransactionImpl : public TransactionBaseImpl {
   // Returns true if locks were stolen successfully, false otherwise.
   bool TryStealingLocks();
 
-  bool IsDeadlockDetect() const { return deadlock_detect_; }
+  bool IsDeadlockDetect() const override { return deadlock_detect_; }
 
   int64_t GetDeadlockDetectDepth() const { return deadlock_detect_depth_; }