Initial steps towards cleaning up integer arithmetic IR.

runtime/vm/flow_graph_optimizer.h

Index: runtime/vm/flow_graph_optimizer.h
diff --git a/runtime/vm/flow_graph_optimizer.h b/runtime/vm/flow_graph_optimizer.h
index 8f6c260c426bfa0f8d0bfdf7e2197e1d7391e8d7..3415b6d45bba6eb4d4727af096b63c1e566b9cff 100644
--- a/runtime/vm/flow_graph_optimizer.h
+++ b/runtime/vm/flow_graph_optimizer.h
@@ -361,12 +361,7 @@ class ConstantPropagator : public FlowGraphVisitor {
     return !IsNonConstant(value) && !IsUnknown(value);
   }
 
-  void HandleBinaryOp(Definition* instr,
-                      Token::Kind op_kind,
-                      const Value& left,
-                      const Value& right);
-
-  void TruncateInteger(Definition* instr, int64_t mask);
+  void VisitBinaryIntegerOp(BinaryIntegerOpInstr* binary_op);
 
   virtual void VisitBlocks() { UNREACHABLE(); }