Turn StringLengthStub (used by string wrappers only) into a hydrogen stub.

src/code-stubs-hydrogen.cc

Index: src/code-stubs-hydrogen.cc
diff --git a/src/code-stubs-hydrogen.cc b/src/code-stubs-hydrogen.cc
index 769f35225ee4578661df5b4194765745ae441b36..e38efca5350c989d544a7dd9e0340bcccd27c3c2 100644
--- a/src/code-stubs-hydrogen.cc
+++ b/src/code-stubs-hydrogen.cc
@@ -608,15 +608,15 @@ Handle<Code> LoadFieldStub::GenerateCode(Isolate* isolate) {
 
 
 template<>
-HValue* CodeStubGraphBuilder<KeyedLoadFieldStub>::BuildCodeStub() {
-  return BuildLoadNamedField(GetParameter(0),
-                             casted_stub()->representation(),
-                             casted_stub()->offset(),
-                             casted_stub()->is_inobject());
+HValue* CodeStubGraphBuilder<StringLengthStub>::BuildCodeStub() {
+  HValue* string = BuildLoadNamedField(
+      GetParameter(0), Representation::Tagged(), JSValue::kValueOffset, true);
+  return BuildLoadNamedField(
+      string, Representation::Tagged(), String::kLengthOffset, true);
 }
 
 
-Handle<Code> KeyedLoadFieldStub::GenerateCode(Isolate* isolate) {
+Handle<Code> StringLengthStub::GenerateCode(Isolate* isolate) {
   return DoGenerateCode(isolate, this);
 }