Rename build-root to library-root

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 5f94f0a99788d55d408409ee862dde3796f09e7e..a708b3c0f0fd7012ffa63e2655d5db28f5bb9fb7 100644
--- a/lib/src/compiler/compiler.dart
+++ b/lib/src/compiler/compiler.dart
@@ -292,8 +292,8 @@ class BuildUnit {
   /// The name of this module.
   final String name;
 
-  /// Build root.  All library names are relative to this path/prefix.
-  final String buildRoot;
+  /// Library root.  All library names are relative to this path/prefix.
+  final String libraryRoot;
 
   /// The list of sources in this module.
   ///
@@ -308,7 +308,7 @@ class BuildUnit {
   // build units.
   final Func1<Source, String> libraryToModule;
 
-  BuildUnit(this.name, this.buildRoot, this.sources, this.libraryToModule);
+  BuildUnit(this.name, this.libraryRoot, this.sources, this.libraryToModule);
 }
 
 /// The output of Dart->JS compilation.