Update range errors to agree on the numbers.

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 "include/dart_api.h"
 #include "vm/exceptions.h"
 #include "vm/dart_api_impl.h"
 #include "vm/isolate.h"
@@ skipping 497 matching lines @@
 
 static uint16_t StringValueAt(const String& str, const Integer& index) {
   if (index.IsSmi()) {
     const intptr_t index_value = Smi::Cast(index).Value();
     if ((0 <= index_value) && (index_value < str.Length())) {
       return str.CharAt(index_value);
     }
   }
 
   // An index larger than Smi is always illegal.
-  Exceptions::ThrowRangeError("index", index, 0, str.Length());
+  Exceptions::ThrowRangeError("index", index, 0, str.Length() - 1);
   return 0;
 }
 
 
 DEFINE_NATIVE_ENTRY(String_charAt, 2) {
   const String& receiver = String::CheckedHandle(arguments->NativeArgAt(0));
   GET_NON_NULL_NATIVE_ARGUMENT(Integer, index, arguments->NativeArgAt(1));
   uint16_t value = StringValueAt(receiver, index);
   return Symbols::FromCharCode(static_cast<int32_t>(value));
 }
@@ skipping 65 matching lines @@
 }
 
 
 DEFINE_NATIVE_ENTRY(StringBuffer_createStringFromUint16Array, 3) {
   GET_NON_NULL_NATIVE_ARGUMENT(TypedData, codeUnits, arguments->NativeArgAt(0));
   GET_NON_NULL_NATIVE_ARGUMENT(Smi, length, arguments->NativeArgAt(1));
   GET_NON_NULL_NATIVE_ARGUMENT(Bool, isLatin1, arguments->NativeArgAt(2));
   intptr_t array_length = codeUnits.Length();
   intptr_t length_value = length.Value();
   if (length_value < 0 || length_value > array_length) {
-    Exceptions::ThrowRangeError("length", length, 0, array_length + 1);
+    Exceptions::ThrowRangeError("length", length, 0, array_length);
   }
   const String& result = isLatin1.value()
       ? String::Handle(OneByteString::New(length_value, Heap::kNew))
       : String::Handle(TwoByteString::New(length_value, Heap::kNew));
   NoSafepointScope no_safepoint;
 
   uint16_t* data_position = reinterpret_cast<uint16_t*>(codeUnits.DataAddr(0));
   String::Copy(result, 0, data_position, length_value);
   return result.raw();
 }
 
 }  // namespace dart