Handle empty string messages in Dart_PostCObject

runtime/vm/dart_api_message.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/dart_api_message.h"
 #include "vm/object.h"
 #include "vm/snapshot_ids.h"
 #include "vm/symbols.h"
 #include "vm/unicode.h"
 
@@ skipping 1168 matching lines @@
       WriteDouble(object->value.as_double);
       break;
     case Dart_CObject_kString: {
       const uint8_t* utf8_str =
           reinterpret_cast<const uint8_t*>(object->value.as_string);
       intptr_t utf8_len = strlen(object->value.as_string);
       if (!Utf8::IsValid(utf8_str, utf8_len)) {
         return false;
       }
 
-      Utf8::Type type;
+      Utf8::Type type = Utf8::kLatin1;
       intptr_t len = Utf8::CodeUnitCount(utf8_str, utf8_len, &type);
-      ASSERT(len > 0);
       if (len > String::kMaxElements) {
         return false;
       }
 
       // Write out the serialization header value for this object.
       WriteInlinedHeader(object);
       // Write out the class and tags information.
       WriteIndexedObject(type == Utf8::kLatin1 ? kOneByteStringCid
                                                : kTwoByteStringCid);
       WriteTags(0);
@@ skipping 130 matching lines @@
     if (!success) {
       UnmarkAllCObjects(object);
       return false;
     }
   }
   UnmarkAllCObjects(object);
   return true;
 }
 
 }  // namespace dart