VM: Speed up output of UTF8 for 1-byte strings.

runtime/vm/raw_object_snapshot.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/native_entry.h"
 #include "vm/object.h"
 #include "vm/object_store.h"
 #include "vm/snapshot.h"
 #include "vm/stub_code.h"
 #include "vm/symbols.h"
@@ skipping 1968 matching lines @@
     }
     *str_obj ^= (*new_symbol)(reader->thread(), ptr, len);
   } else {
     // Set up the string object.
     *str_obj = StringType::New(len, HEAP_SPACE(kind));
     str_obj->SetHash(0);  // Will get computed when needed.
     if (len == 0) {
       return;
     }
     NoSafepointScope no_safepoint;
-    CharacterType* str_addr = StringType::CharAddr(*str_obj, 0);
+    CharacterType* str_addr = StringType::DataStart(*str_obj);
     for (intptr_t i = 0; i < len; i++) {
       *str_addr = reader->Read<CharacterType>();
       str_addr++;
     }
   }
 }
 
 RawOneByteString* OneByteString::ReadFrom(SnapshotReader* reader,
                                           intptr_t object_id,
                                           intptr_t tags,
@@ skipping 934 matching lines @@
     // We do not allow objects with native fields in an isolate message.
     writer->SetWriteException(Exceptions::kArgument,
                               "Illegal argument in isolate message"
                               " : (object is a UserTag)");
   } else {
     UNREACHABLE();
   }
 }
 
 }  // namespace dart