These now appear on internals as takeServicesProvidedToEmbedder and
takeServicesProvidedByEmbedder. When you call these functions, you get back the
raw int that represents the handle. We'll need to wrap them up inside the Dart
VM with the appropriate types. We can create a nice wrapper for that in a
future CL.

R=hansmuller@google.com, hansmuller@chromium.org

Review URL: https://codereview.chromium.org/944733002