Restructure Add and SetAt to not create a Handle.

lib/string.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/bootstrap_natives.h"
 
 #include "vm/exceptions.h"
 #include "vm/native_entry.h"
 #include "vm/object.h"
 #include "vm/symbols.h"
@@ skipping 76 matching lines @@
       GrowableObjectArray::New(16, Heap::kNew));
   String& str = String::Handle(isolate);
   intptr_t start = 0;
   intptr_t i = 0;
   for (; i < len; i++) {
     if (split_code == OneByteString::CharAt(receiver, i)) {
       str = OneByteString::SubStringUnchecked(receiver,
                                               start,
                                               (i - start),
                                               Heap::kNew);
-      result.Add(isolate, str);
+      result.Add(str);
       start = i + 1;
     }
   }
   str = OneByteString::SubStringUnchecked(receiver,
                                           start,
                                           (i - start),
                                           Heap::kNew);
-  result.Add(isolate, str);
+  result.Add(str);
   return result.raw();
 }
 
 
 DEFINE_NATIVE_ENTRY(String_getHashCode, 1) {
   const String& receiver = String::CheckedHandle(arguments->NativeArgAt(0));
   intptr_t hash_val = receiver.Hash();
   ASSERT(hash_val > 0);
   ASSERT(Smi::IsValid(hash_val));
   return Smi::New(hash_val);
@@ skipping 77 matching lines @@
     if (!elem.IsString()) {
       GrowableArray<const Object*> args;
       args.Add(&elem);
       Exceptions::ThrowByType(Exceptions::kArgument, args);
     }
   }
   return String::ConcatAll(strings);
 }
 
 }  // namespace dart