VM: Optimized code for all of [External]{One|Two}ByteString::codeUnitAt.

runtime/vm/object.cc

 // Copyright (c) 2012, 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/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 15513 matching lines @@
     case kExternalTwoByteStringCid:
       return ExternalTwoByteString::kBytesPerElement;
     default:
       UNIMPLEMENTED();
       return 0;
   }
 }
 
 
 intptr_t Instance::DataOffsetFor(intptr_t cid) {
-  if (RawObject::IsExternalTypedDataClassId(cid)) {
+  if (RawObject::IsExternalTypedDataClassId(cid) ||
+      RawObject::IsExternalStringClassId(cid)) {
     // Elements start at offset 0 of the external data.
     return 0;
   }
   if (RawObject::IsTypedDataClassId(cid)) {
     return TypedData::data_offset();
   }
   switch (cid) {
     case kArrayCid:
     case kImmutableArrayCid:
       return Array::data_offset();
@@ skipping 6907 matching lines @@
   return UserTag::null();
 }
 
 
 const char* UserTag::ToCString() const {
   const String& tag_label = String::Handle(label());
   return tag_label.ToCString();
 }
 
 }  // namespace dart