Correctly set kCanBeDivByZero flag for HMathFloorOfDiv.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index 7988d2f25968c851c9074c38d8043fb7f18ebfc6..dc899b43a7daf4cab2925a63510a854efc5fcb90 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -3111,6 +3111,9 @@ class HMathFloorOfDiv: public HBinaryOperation {
     set_representation(Representation::Integer32());
     SetFlag(kUseGVN);
     SetFlag(kCanOverflow);
+    if (!right->IsConstant()) {
+      SetFlag(kCanBeDivByZero);
+    }
   }
 
   virtual HValue* EnsureAndPropagateNotMinusZero(BitVector* visited);