Use regular map-checks to guard string-length loading.

src/x64/stub-cache-x64.cc

Index: src/x64/stub-cache-x64.cc
diff --git a/src/x64/stub-cache-x64.cc b/src/x64/stub-cache-x64.cc
index f3497ddfc8f9e5c667760409b188731a3f54eb05..6cd24879354452b9070a0ae330ce08f45e83b4d3 100644
--- a/src/x64/stub-cache-x64.cc
+++ b/src/x64/stub-cache-x64.cc
@@ -304,32 +304,28 @@ void StubCompiler::GenerateLoadStringLength(MacroAssembler* masm,
                                             Register receiver,
                                             Register scratch1,
                                             Register scratch2,
-                                            Label* miss,
-                                            bool support_wrappers) {
+                                            Label* miss) {
   Label check_wrapper;
 
   // Check if the object is a string leaving the instance type in the
   // scratch register.
-  GenerateStringCheck(masm, receiver, scratch1, miss,
-                      support_wrappers ? &check_wrapper : miss);
+  GenerateStringCheck(masm, receiver, scratch1, miss, &check_wrapper);
 
   // Load length directly from the string.
   __ movq(rax, FieldOperand(receiver, String::kLengthOffset));
   __ ret(0);
 
-  if (support_wrappers) {
-    // Check if the object is a JSValue wrapper.
-    __ bind(&check_wrapper);
-    __ cmpl(scratch1, Immediate(JS_VALUE_TYPE));
-    __ j(not_equal, miss);
+  // Check if the object is a JSValue wrapper.
+  __ bind(&check_wrapper);
+  __ cmpl(scratch1, Immediate(JS_VALUE_TYPE));
+  __ j(not_equal, miss);
 
-    // Check if the wrapped value is a string and load the length
-    // directly if it is.
-    __ movq(scratch2, FieldOperand(receiver, JSValue::kValueOffset));
-    GenerateStringCheck(masm, scratch2, scratch1, miss, miss);
-    __ movq(rax, FieldOperand(scratch2, String::kLengthOffset));
-    __ ret(0);
-  }
+  // Check if the wrapped value is a string and load the length
+  // directly if it is.
+  __ movq(scratch2, FieldOperand(receiver, JSValue::kValueOffset));
+  GenerateStringCheck(masm, scratch2, scratch1, miss, miss);
+  __ movq(rax, FieldOperand(scratch2, String::kLengthOffset));
+  __ ret(0);
 }