Add the concept of a client ID which is used to identify a specific (one of several) clients in all API calls. (cherry-pick ofaa36f07194, Change-Id: I43f13d51bee8b57c6d0ba1174168288b8d6c21c5) Bug: 26962024 Change-Id: I0e0ddf37ea9800ae97115d6af384b54b49a40d74 (cherry picked from commit5155990c09)