Qualify library names in packages

lib/src/compiler/compiler.dart

Index: lib/src/compiler/compiler.dart
diff --git a/lib/src/compiler/compiler.dart b/lib/src/compiler/compiler.dart
index 41a05f72b3927b949dfcf08176856255bc536018..969cd6d3418fe877024ea24b64ff2cdede1b7a08 100644
--- a/lib/src/compiler/compiler.dart
+++ b/lib/src/compiler/compiler.dart
@@ -196,6 +196,9 @@ class BuildUnit {
   /// The name of this module.
   final String name;
 
+  /// Build root.  All library names are relative to this path/prefix.
+  final String buildRoot;
+
   /// The list of sources in this module.
   ///
   /// The set of Dart files can be arbitrarily large, but it must contain
@@ -209,7 +212,7 @@ class BuildUnit {
   // build units.
   final Func1<Source, String> libraryToModule;
 
-  BuildUnit(this.name, this.sources, this.libraryToModule);
+  BuildUnit(this.name, this.buildRoot, this.sources, this.libraryToModule);
 }
 
 /// The output of Dart->JS compilation.