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

src/arm64/full-codegen-arm64.cc

Index: src/arm64/full-codegen-arm64.cc
diff --git a/src/arm64/full-codegen-arm64.cc b/src/arm64/full-codegen-arm64.cc
index 8ccf4a1011dc0613a6ded13b05d1e9ca6cf50c7f..3e8026f3248a35ff1737e67dcfa89972ee308ec6 100644
--- a/src/arm64/full-codegen-arm64.cc
+++ b/src/arm64/full-codegen-arm64.cc
@@ -4708,9 +4708,11 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
     __ B(&stub_call);
     __ Bind(&slow);
   }
-  ToNumberStub convert_stub(isolate());
-  __ CallStub(&convert_stub);
-  PrepareForBailoutForId(expr->ToNumberId(), TOS_REG);
+  if (!is_strong(language_mode())) {
+    ToNumberStub convert_stub(isolate());
+    __ CallStub(&convert_stub);
+    PrepareForBailoutForId(expr->ToNumberId(), TOS_REG);
+  }
 
   // Save result for postfix expressions.
   if (expr->is_postfix()) {
@@ -4755,6 +4757,9 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
   }
   __ Bind(&done);
 
+  if (is_strong(language_mode())) {
+    PrepareForBailoutForId(expr->ToNumberId(), TOS_REG);
+  }
   // Store the value returned in x0.
   switch (assign_type) {
     case VARIABLE: