Make isComplete reflect result availability (#178)

Fixes #176

Change the `CancelableOperation.isComplete` to forward to the `_inner`
completer, which is not completed until the result is available unlike
`CancelableOperation.isComplete` which may lead the result when
`complete` is called with a `Future` argument. Update the docs to
reflect the new behavior. Keep the detail about this property indicating
whether the operation can still be canceled. This detail was incorrectly
stated before, but matches the new implementation.

Remove details pointing to `CancelableCompleter` from the
`CancelableOperation` docs. Flesh out the docs on the completer so that
the distinction between the two `isComplete` getters is more clear.

Remove a detail about not returning `null` from the `cancel()` doc since
the non-nullable return type already makes this clear.
3 files changed
tree: 8f85e057a69de39bc2d64ffa51f298bfc331d629
  1. .github/
  2. lib/
  3. test/
  4. .gitignore
  5. analysis_options.yaml
  10. pubspec.yaml

Contains utility classes in the style of dart:async to work with asynchronous computations.