Merge TRUNCDIV and MOD into TRUNCDIV_MOD single operation.

runtime/vm/flow_graph_optimizer.h

Index: runtime/vm/flow_graph_optimizer.h
===================================================================
--- runtime/vm/flow_graph_optimizer.h	(revision 30236)
+++ runtime/vm/flow_graph_optimizer.h	(working copy)
@@ -31,7 +31,8 @@
 
   // Optimize (a << b) & c pattern: if c is a positive Smi or zero, then the
   // shift can be a truncating Smi shift-left and result is always Smi.
-  void TryOptimizeLeftShiftWithBitAndPattern();
+  // Merge truncdiv/mod pattern.
+  void TryOptimizePatterns();
 
   // Returns true if any instructions were canonicalized away.
   bool Canonicalize();
@@ -203,6 +204,7 @@
   void OptimizeLeftShiftBitAndSmiOp(Definition* bit_and_instr,
                                     Definition* left_instr,
                                     Definition* right_instr);
+  void TryMergeDivMod(BinarySmiOpInstr* truncdiv_instr);
 
   FlowGraph* flow_graph_;