Currently each call to Task.forResult(null) and Task.cancelled() create new instances of Task and TaskCompletionSource, which are exactly the same for each execution.

These methods can be extremely common in codebases, especially Task.forResult(null), which is used internally in Bolts-Android and Parse-SDK-Android from converting null return values in continuations to stubbing non-asynchronous methods with an asynchronous method signature.

We can optimize these calls by reusing the same value and reduce the amount of memory allocated in applications relying on Bolts and we can do this since each return value is equivalent and essentially immutable.

/cc @nlutsenko