[strong] Implement strong mode semantics for the count operation.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index c876bd50fafd803c19578bb898440352d5689e7b..2a969fc6a2675b801e7a5df36ae0030012955c1f 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -4151,7 +4151,7 @@ class HBitwiseBinaryOperation : public HBinaryOperation {
       : HBinaryOperation(context, left, right, strength, type) {
     SetFlag(kFlexibleRepresentation);
     SetFlag(kTruncatingToInt32);
-    SetFlag(kAllowUndefinedAsNaN);
+    if (!is_strong(strength)) SetFlag(kAllowUndefinedAsNaN);
     SetAllSideEffects();
   }
 
@@ -4232,7 +4232,7 @@ class HArithmeticBinaryOperation : public HBinaryOperation {
                          HType::TaggedNumber()) {
     SetAllSideEffects();
     SetFlag(kFlexibleRepresentation);
-    SetFlag(kAllowUndefinedAsNaN);
+    if (!is_strong(strength)) SetFlag(kAllowUndefinedAsNaN);
   }
 
   void RepresentationChanged(Representation to) override {