Remove barback from the repo.

pkg/barback/CHANGELOG.md

-## 0.15.2+2
-
-* Fix a bug in listing all assets from a static package.
-
-## 0.15.2+1
-
-* Properly handle logs from a transformer that's been canceled.
-
-## 0.15.2
-
-* Add a `StaticPackageProvider` class to more efficiently handle immutable,
-  untransformed packages.
-
-## 0.15.0+1
-
-* Widen the version constraint on the `collection` package.
-
-## 0.15.0
-
-* Fully switch from `source_maps`' `Span` class to `source_span`'s `SourceSpan`
-  class.
-
-## 0.14.2
-
-* All TransformLogger methods now accept SourceSpans from the source_span
-  package in addition to Spans from the source_maps package. In 0.15.0, only
-  SourceSpans will be accepted.
-
-## 0.14.1+3
-
-* Add a dependency on the `pool` package.
-
-## 0.14.1+2
-
-* Automatically log how long it takes long-running transforms to run.
-
-## 0.14.1+1
-
-* Fix a bug where an event could be added to a closed stream.
-
-## 0.14.1
-
-* Add an `AggregateTransformer` type. Aggregate transformers transform groups of
-  assets for which no single asset is primary. For example, one could be used to
-  merge all images in a directory into a single file.
-
-* Add a `message` getter to `TransformerException` and `AssetLoadException`.
-
-* Fix a bug where transformers would occasionally emit stale output after their
-  inputs changed.
-
-## 0.14.0+3
-
-* Properly handle synchronous errors in `PackageProvider.getAsset()`.
-
-## 0.14.0+2
-
-* Fix a bug with the previous bug fix.
-
-## 0.14.0+1
-
-* Fix a bug where a transformer group preceded by another transformer group
-  would sometimes fail to load secondary assets.
-
-## 0.14.0
-
-* **Breaking change**: when an output of a lazy transformer is requested, that
-  transformer will run long enough to generate the output, then become lazy
-  again. Previously, it would become eager as soon as an asset had been
-  requested.
-
-* Only run `Transformer.isPrimary` and `Transformer.declareOutputs` once for
-  each asset.
-
-* Lazy transformers' laziness is preserved when followed by
-  declaring transformers, or by normal transformers for which the lazy outputs
-  aren't primary.
-
-* Fix a bug where reading the primary input using `Transform.readInputAsString`
-  had slightly different behavior than reading it using
-  `Transform.primary.readAsString`.
-
-* Fix a crashing bug when `Barback.getAllAssets` is called synchronously after
-  creating a new `Barback` instance.
-
-* Don't warn if a lazy or declaring transformer doesn't emit outputs that it has
-  declared. This is valid for transformers like dart2js that need to read their
-  primary input in order to determine whether they should run.
-
-* Allow `Transformer.isPrimary`, `Transformer.apply`, and
-  `DeclaringTransformer.declareOutputs` to return non-`Future` values if they
-  run synchronously.
-
-* Fix a deadlock bug when a lazy primary input to a lazy transformer became
-  dirty while the transformer's `apply` method was running.
-
-* Run declaring transformers with lazy inputs eagerly if the inputs become
-  available.
-
-## 0.13.0
-
-* `Transformer.isPrimary` now takes an `AssetId` rather than an `Asset`.
-
-* `DeclaringTransform` now only exposes the primary input's `AssetId`, rather
-  than the primary `Asset` object.
-
-* `DeclaringTransform` no longer supports `getInput`, `readInput`,
-  `readInputAsString`, or `hasInput`.
-
-## 0.12.0
-
-* Add a `Transform.logger.fine` function that doesn't print its messages by
-  default. When using Barback with pub in verbose mode, these messages will be
-  printed.
-
-* Add a `Transform.hasInput` function that returns whether or not a given
-  secondary input exists.
-
-* `Transformer.allowedExtensions` now supports extensions containing multiple
-  periods, such as `.dart.js`.
-
-* Transforms now pass their primary inputs through to the next phase by default.
-  A transformer may still overwrite its primary input without causing a
-  collision. If a transformer doesn't overwrite its primary input, it may cause
-  it not to be passed through by calling `Transform.consumePrimary`. The primary
-  input will be consumed by default if a transformer throws an error.
-
-* If an input requested with `Transform.getInput`, `Transform.readInput`, or
-  `Transform.readInputAsString` cannot be found, an `AssetNotFoundException`
-  will be thrown. This was always what the documentation said, but previously a
-  `MissingInputException` was thrown instead.
-
-* If a transformer calls `Transform.logger.error`, the transformer will now be
-  considered to have failed after it finishes running `apply()`. This means that
-  its outputs will not be consumed by future transformers and its primary input
-  will not be passed through to the next phase.
-
-* If a transform calls `Transform.getInput`, `Transform.readInput`,
-  `Transform.readInputAsString`, or `Transform.hasInput` on an input that
-  doesn't exist, the transform will be re-run if that input is created in the
-  future.