Make StringBase._substringUnchecked a native function.

runtime/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 36 matching lines @@
     result ^= OneByteString::New(temp, len, Heap::kNew);
   } else if (is_two_byte_string) {
     result ^= TwoByteString::New(temp, len, Heap::kNew);
   } else {
     result ^= FourByteString::New(temp, len, Heap::kNew);
   }
   arguments->SetReturn(result);
 }
 
 
+DEFINE_NATIVE_ENTRY(StringBase_substringUnchecked, 3) {
+  GET_NATIVE_ARGUMENT(String, receiver, arguments->At(0));
+  GET_NATIVE_ARGUMENT(Smi, start_obj, arguments->At(1));
+  GET_NATIVE_ARGUMENT(Smi, end_obj, arguments->At(2));
+
+  intptr_t start = start_obj.Value();
+  intptr_t end = end_obj.Value();
+
+  const String& result = String::Handle(
+      String::SubString(receiver, start, (end - start)));
+  arguments->SetReturn(result);
+}
+
+
+
 DEFINE_NATIVE_ENTRY(String_hashCode, 1) {
   const String& receiver = String::CheckedHandle(arguments->At(0));
   intptr_t hash_val = receiver.Hash();
   ASSERT(hash_val > 0);
   ASSERT(Smi::IsValid(hash_val));
   const Smi& hash_smi = Smi::Handle(Smi::New(hash_val));
   arguments->SetReturn(hash_smi);
 }
 
 
@@ skipping 81 matching lines @@
       GrowableArray<const Object*> args;
       args.Add(&elem);
       Exceptions::ThrowByType(Exceptions::kIllegalArgument, args);
     }
   }
   const String& result = String::Handle(String::ConcatAll(strings));
   arguments->SetReturn(result);
 }
 
 }  // namespace dart