Work outlined in document: https://docs.google.com/document/d/1oNLxJr_ZqjENVhF94-PqxsGPx0qGXx-pRJxXL6LSagc/edit#

• Add performance tests
• Embedder copy
  • Pass ownership of message memory to embedder when receiving messages from flutter
  • Pass ownership of message memory to the engine when sending results from embedder
• Dart VM copy
  • Pass ownership of message from dart vm to engine when receiving a message from flutter (typedata)
  • Pass ownership of message from engine to dart vm when sending response a message to flutter (typedata)