Added support for exports and re-exports.

lib/compiler/implementation/tree/nodes.dart

Index: lib/compiler/implementation/tree/nodes.dart
diff --git a/lib/compiler/implementation/tree/nodes.dart b/lib/compiler/implementation/tree/nodes.dart
index 398e30a1c96f282b1e81a667524eefba77bc407c..43ee30140eb1531451162c662f0350c0f0595360 100644
--- a/lib/compiler/implementation/tree/nodes.dart
+++ b/lib/compiler/implementation/tree/nodes.dart
@@ -1642,14 +1642,20 @@ class LibraryName extends LibraryTag {
   Token getEndToken() => name.getEndToken().next;
 }
 
-class Import extends LibraryTag {
+abstract class ImportExport extends LibraryTag {

[Lasse Reichstein Nielsen, 2012/09/28 07:45:36]

Call it LibraryDependency (or something better if you have it).
Add doc-comment: This tag describes a dependency between one library and the
exported identifiers of another library. The other library is specified by the
[uri]. Combinators filter away some identifiers from the other library.

[Johnni Winther, 2012/10/09 09:47:10]

Done.

   final LiteralString uri;
-  final Identifier prefix;
   final NodeList combinators;
 
+  ImportExport(this.uri, this.combinators);
+}
+
+class Import extends ImportExport {

[Lasse Reichstein Nielsen, 2012/09/28 07:45:36]

Comment to the effect that an Import is dependency on another library where the
exported identifiers are put into the import scope of the importing library. The
import scope is only visible inside the library.

[Johnni Winther, 2012/10/09 09:47:10]

Done.

+  final Identifier prefix;
   final Token importKeyword;
 
-  Import(this.importKeyword, this.uri, this.prefix, this.combinators);
+  Import(this.importKeyword, LiteralString uri,
+         this.prefix, NodeList combinators)
+      : super(uri, combinators);
 
   bool get isImport => true;
 
@@ -1672,13 +1678,11 @@ class Import extends LibraryTag {
   }
 }
 
-class Export extends LibraryTag {
-  final LiteralString uri;
-  final NodeList combinators;
-
+class Export extends ImportExport {

[Lasse Reichstein Nielsen, 2012/09/28 07:45:36]

And a comment too, describing what an export is relative to a LibraryDependency.

[Johnni Winther, 2012/10/09 09:47:10]

Done.

   final Token exportKeyword;
 
-  Export(this.exportKeyword, this.uri, this.combinators);
+  Export(this.exportKeyword, LiteralString uri, NodeList combinators)
+      : super(uri, combinators);
 
   bool get isExport => true;