Instead of using the default `global.Promise` object, it's common to allow users to provide their own Promise-spec compliant library (e.g. [bluebird](http://gitnpm.com/bluebird)). We used to do this in non-GAPIC/gax clients, but transferring over to GAPIC-only broke the functionality: https://github.com/googleapis/nodejs-pubsub/issues/17
Instead of using the default
global.Promiseobject, it's common to allow users to provide their own Promise-spec compliant library (e.g. bluebird).We used to do this in non-GAPIC/gax clients, but transferring over to GAPIC-only broke the functionality: googleapis/nodejs-pubsub#17