Stop running pub get at gclient sync time and fix build bugs

mojo/public/dart/third_party/barback/CHANGELOG.md

Index: mojo/public/dart/third_party/barback/CHANGELOG.md
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+## 0.15.2+6
+
+* Fix a deadlock that occurred occasionally when a declaring transformer was
+  followed by a lazy transformer (most commonly `$dart2js`).
+
+## 0.15.2+5
+
+* If a transformer requests a non-existent asset from another package, it will
+  now be re-run if that asset is later created.
+
+## 0.15.2+4
+
+* Fix an incorrect example.
+
+## 0.15.2+3
+
+* Clarify that a transform may emit any number of outputs.
+
+## 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.