[mojo] Allow value deserialization to fail

mojo/public/cpp/bindings/lib/string_serialization.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "mojo/public/cpp/bindings/lib/string_serialization.h"
 
 #include <string.h>
 
 namespace mojo {
 
@@ skipping 10 matching lines @@
     internal::String_Data* result =
         internal::String_Data::New(input.size(), buf);
     if (result)
       memcpy(result->storage(), input.data(), input.size());
     *output = result;
   } else {
     *output = nullptr;
   }
 }
 
-void Deserialize_(internal::String_Data* input,
+bool Deserialize_(internal::String_Data* input,
                   String* output,
                   internal::SerializationContext* context) {
   if (input) {
     String result(input->storage(), input->size());
     result.Swap(output);
   } else {
     output->reset();
   }
+  return true;
 }
 
 }  // namespace mojo