Get rid of the unused native code StringAddStub.

src/isolate.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2094 matching lines @@
     stub.InitializeInterfaceDescriptor(
         this, code_stub_interface_descriptor(CodeStub::FastCloneShallowArray));
     BinaryOpICStub::InstallDescriptors(this);
     BinaryOpWithAllocationSiteStub::InstallDescriptors(this);
     CompareNilICStub::InitializeForIsolate(this);
     ToBooleanStub::InitializeForIsolate(this);
     ArrayConstructorStubBase::InstallDescriptors(this);
     InternalArrayConstructorStubBase::InstallDescriptors(this);
     FastNewClosureStub::InstallDescriptors(this);
     NumberToStringStub::InstallDescriptors(this);
-    NewStringAddStub::InstallDescriptors(this);
+    StringAddStub::InstallDescriptors(this);
   }
 
   CallDescriptors::InitializeForIsolate(this);
 
   initialized_from_snapshot_ = (des != NULL);
 
   return true;
 }
 
 
@@ skipping 182 matching lines @@
 
 #ifdef DEBUG
 #define ISOLATE_FIELD_OFFSET(type, name, ignored)                       \
 const intptr_t Isolate::name##_debug_offset_ = OFFSET_OF(Isolate, name##_);
 ISOLATE_INIT_LIST(ISOLATE_FIELD_OFFSET)
 ISOLATE_INIT_ARRAY_LIST(ISOLATE_FIELD_OFFSET)
 #undef ISOLATE_FIELD_OFFSET
 #endif
 
 } }  // namespace v8::internal