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

src/mips64/full-codegen-mips64.cc

Index: src/mips64/full-codegen-mips64.cc
diff --git a/src/mips64/full-codegen-mips64.cc b/src/mips64/full-codegen-mips64.cc
index 62991c9eaac39b7041569835f2d3bdbcc9d8aec4..764bced5cacb7c766a2eefd58cf38b0cb6e26f12 100644
--- a/src/mips64/full-codegen-mips64.cc
+++ b/src/mips64/full-codegen-mips64.cc
@@ -5041,9 +5041,11 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
     __ jmp(&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()) {
@@ -5084,6 +5086,9 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
   patch_site.EmitPatchInfo();
   __ bind(&done);
 
+  if (is_strong(language_mode())) {
+    PrepareForBailoutForId(expr->ToNumberId(), TOS_REG);
+  }
   // Store the value returned in v0.
   switch (assign_type) {
     case VARIABLE: