[turbofan] Lower StringCharCodeAt to a dedicated builtin.

src/interface-descriptors.cc

Index: src/interface-descriptors.cc
diff --git a/src/interface-descriptors.cc b/src/interface-descriptors.cc
index 49e58f619e8fc834a4f4eb061140e32b050b7852..cfb88672c69e7fa3a4ffbf36a8a3ce99bcbfd280 100644
--- a/src/interface-descriptors.cc
+++ b/src/interface-descriptors.cc
@@ -198,6 +198,21 @@ void StringCharAtDescriptor::InitializePlatformSpecific(
   DefaultInitializePlatformSpecific(data, kParameterCount);
 }
 
+void StringCharCodeAtDescriptor::InitializePlatformIndependent(
+    CallInterfaceDescriptorData* data) {
+  // kReceiver, kPosition
+  // TODO(turbofan): Allow builtins to return untagged values.
+  MachineType machine_types[] = {MachineType::AnyTagged(),
+                                 MachineType::IntPtr()};
+  data->InitializePlatformIndependent(arraysize(machine_types), 0,
+                                      machine_types);
+}
+
+void StringCharCodeAtDescriptor::InitializePlatformSpecific(
+    CallInterfaceDescriptorData* data) {
+  DefaultInitializePlatformSpecific(data, kParameterCount);
+}
+
 void StringCompareDescriptor::InitializePlatformSpecific(
     CallInterfaceDescriptorData* data) {
   Register registers[] = {LeftRegister(), RightRegister()};