Support Dart core libraries in source maps.

sdk/lib/_internal/pub/lib/src/barback/pub_package_provider.dart

Index: sdk/lib/_internal/pub/lib/src/barback/pub_package_provider.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/pub_package_provider.dart b/sdk/lib/_internal/pub/lib/src/barback/pub_package_provider.dart
index dd90b9f688a947de75b58271af16c86126708d41..1665be9d538da3d3c4db8d5e71e1673dfe779d42 100644
--- a/sdk/lib/_internal/pub/lib/src/barback/pub_package_provider.dart
+++ b/sdk/lib/_internal/pub/lib/src/barback/pub_package_provider.dart
@@ -9,8 +9,9 @@ import 'dart:async';
 import 'package:barback/barback.dart';
 import 'package:path/path.dart' as path;
 
-import '../package_graph.dart';
 import '../io.dart';
+import '../package_graph.dart';
+import '../sdk.dart' as sdk;
 
 /// An implementation of barback's [PackageProvider] interface so that barback
 /// can find assets within pub packages.
@@ -20,22 +21,38 @@ class PubPackageProvider implements PackageProvider {
 
   PubPackageProvider(PackageGraph graph)
       : _graph = graph,
-        packages = new List.from(graph.packages.keys)..add(r"$pub");
+        packages = [r"$pub", r"$sdk"]..addAll(graph.packages.keys);
 
   Future<Asset> getAsset(AssetId id) {
-    if (id.package != r'$pub') {
-      var nativePath = path.fromUri(id.path);
-      var file = path.join(_graph.packages[id.package].dir, nativePath);
+    // "$pub" is a psuedo-package that allows pub's transformer-loading
+    // infrastructure to share code with pub proper.
+    if (id.package == r'$pub') {
+      var components = path.url.split(id.path);
+      assert(components.isNotEmpty);
+      assert(components.first == 'lib');
+      components[0] = 'dart';
+      var file = assetPath(path.joinAll(components));
       return new Future.value(new Asset.fromPath(id, file));
     }
 
-    // "$pub" is a psuedo-package that allows pub's transformer-loading
-    // infrastructure to share code with pub proper.
-    var components = path.url.split(id.path);
-    assert(components.isNotEmpty);
-    assert(components.first == 'lib');
-    components[0] = 'dart';
-    var file = assetPath(path.joinAll(components));
+    // "$sdk" is a pseudo-package that provides access to the Dart library
+    // sources in the SDK. The dart2js transformer uses this to locate the Dart
+    // sources for "dart:" libraries.
+    if (id.package == r'$sdk') {
+      // The asset path contains two "lib" entries. The first represent's pub's
+      // concept that all public assets are in "lib". The second comes from the
+      // organization of the SDK itself. Strip off the first. Leave the second
+      // since dart2js adds it and expects it to be there.
+      var parts = path.split(path.fromUri(id.path));
+      assert(parts.isNotEmpty && parts[0] == 'lib');
+      parts = parts.skip(1);
+
+      var file = path.join(sdk.rootDirectory, path.joinAll(parts));
+      return new Future.value(new Asset.fromPath(id, file));
+    }
+
+    var nativePath = path.fromUri(id.path);
+    var file = path.join(_graph.packages[id.package].dir, nativePath);
     return new Future.value(new Asset.fromPath(id, file));
   }
 }