add 'imports' field for OutputUnitInfo

lib/info.dart

Index: lib/info.dart
diff --git a/lib/info.dart b/lib/info.dart
index 5e79a70e973fd0fbf084ecb364fd985dd61b0635..0ca08cab01e621246647105ea979df5be824708b 100644
--- a/lib/info.dart
+++ b/lib/info.dart
@@ -202,7 +202,11 @@ class LibraryInfo extends BasicInfo {
 /// program unless the application uses deferred imports, in which case there
 /// would be an additional output unit per deferred chunk.
 class OutputUnitInfo extends BasicInfo {
+  /// The deferred imports that will load this output unit.
+  List<String> imports = <String>[];

[Siggi Cherem (dart-lang), 2015/11/04 03:33:16]

Oh funny, my initial thought was that you meant "imports" as the list of shared
outputunitinfos that this info needs, but this makes more sense :). I'm ok with
the current name, another idea if you prefer would be `loadingImports`? up to
you.

[Harry Terkelsen, 2015/11/12 19:21:01]

I'm keeping it as imports to match the name in dart2js

+
   static int _ids = 0;
+
   OutputUnitInfo(String name, int size)
       : super(InfoKind.outputUnit, _ids++, name, null, size, null);