Refactor the Transform classes.

Refactor the Transform classes.

This adds a more principled way of exposing only the necessary API to the
Transformer while providing detailed information to the TransformNode. It lays
the groundwork for [consumePrimary].

R=rnystrom@google.com
BUG=16612
Committed: https://code.google.com/p/dart/source/detail?r=33449

[Bob Nystrom, 2014-02-27 23:41:18]

Couple of questions, but I <3 this. LGTM.

https://codereview.chromium.org/178223024/diff/1/pkg/barback/lib/src/transfor...
File pkg/barback/lib/src/transform_node.dart (right):

https://codereview.chromium.org/178223024/diff/1/pkg/barback/lib/src/transfor...
pkg/barback/lib/src/transform_node.dart:210: var newOutputs = new
AssetSet.from(transformController.outputs);
outputs already is an AssetSet. Is there a reason to copy it here?

https://codereview.chromium.org/178223024/diff/1/pkg/barback/lib/src/transfor...
pkg/barback/lib/src/transform_node.dart:256: var newIds = new
Set.from(transformController.outputIds);
Ditto. Why copy the set here?

[nweiz, 2014-02-28 01:19:08]

https://codereview.chromium.org/178223024/diff/1/pkg/barback/lib/src/transfor...
File pkg/barback/lib/src/transform_node.dart (right):

https://codereview.chromium.org/178223024/diff/1/pkg/barback/lib/src/transfor...
pkg/barback/lib/src/transform_node.dart:210: var newOutputs = new
AssetSet.from(transformController.outputs);
On 2014/02/27 23:41:18, Bob Nystrom wrote:
> outputs already is an AssetSet. Is there a reason to copy it here?

It just felt kind of weird to modify another class's instance variable. I'm
happy to change it to access the set directly if yuo think that's cleaner.

[Bob Nystrom, 2014-02-28 18:56:39]

https://codereview.chromium.org/178223024/diff/1/pkg/barback/lib/src/transfor...
File pkg/barback/lib/src/transform_node.dart (right):

https://codereview.chromium.org/178223024/diff/1/pkg/barback/lib/src/transfor...
pkg/barback/lib/src/transform_node.dart:210: var newOutputs = new
AssetSet.from(transformController.outputs);
On 2014/02/28 01:19:08, nweiz wrote:
> On 2014/02/27 23:41:18, Bob Nystrom wrote:
> > outputs already is an AssetSet. Is there a reason to copy it here?
> 
> It just felt kind of weird to modify another class's instance variable. I'm
> happy to change it to access the set directly if yuo think that's cleaner.

I look at it more like claiming ownership. It feels a bit weird to me too, but
in this case the owning object is discarded immediately after this. Not copying
is a little faster and (more important to me) a little less code.

[nweiz, 2014-03-07 20:32:54]

Committed patchset #1 manually as r33449 (presubmit successful).