Allow dart2dart to output one file per library.

sdk/lib/_internal/compiler/implementation/tree/unparser.dart

Index: sdk/lib/_internal/compiler/implementation/tree/unparser.dart
diff --git a/sdk/lib/_internal/compiler/implementation/tree/unparser.dart b/sdk/lib/_internal/compiler/implementation/tree/unparser.dart
index ce0b60eea650579556b9dc6aea7c829b60ce8449..97e3aaed1f6ddacc60db94404b41841d8646e12d 100644
--- a/sdk/lib/_internal/compiler/implementation/tree/unparser.dart
+++ b/sdk/lib/_internal/compiler/implementation/tree/unparser.dart
@@ -641,12 +641,21 @@ class Unparser extends Indentation implements Visitor {
     indentLess();
   }
 
-  unparseImportTag(String uri, [String prefix]) {
-    final suffix = prefix == null ? '' : ' as $prefix';
+  unparseImportTag(String uri, {String prefix, List<String> shows: const [],

[jgruber1, 2014/08/15 06:20:53]

Types on these and suffix? :)

[sigurdm, 2014/08/15 13:31:42]

Done.

+      bool isDeferred: false}) {
+    final suffix = (isDeferred ? ' deferred' : '') +

[Johnni Winther, 2014/08/15 08:07:31]

Use interpolation instead of the + operator on String.

[sigurdm, 2014/08/15 13:31:42]

Done.

+        (prefix == null ? '' : ' as $prefix') +
+        (shows.isEmpty ? '' : ' show ${shows.join(", ")}');
     write('import "$uri"$suffix;');
     newline();
   }
 
+  unparseExportTag(String uri, {List<String> shows: const []}) {
+    final suffix = shows.isEmpty ? '' : ' show ${shows.join(", ")}';
+    write('export "$uri"$suffix;');
+    newline();
+  }
+
   visitTryStatement(TryStatement node) {
     addToken(node.tryKeyword);
     visit(node.tryBlock);