Lazily throw pubspec parsing exceptions.

sdk/lib/_internal/pub/lib/src/source/hosted.dart

Index: sdk/lib/_internal/pub/lib/src/source/hosted.dart
diff --git a/sdk/lib/_internal/pub/lib/src/source/hosted.dart b/sdk/lib/_internal/pub/lib/src/source/hosted.dart
index b2c1647cebab86b4979bcbf9f65934f9a5a8e4fe..af110e6f582d35cd24433fffe5c0c75c7b549be5 100644
--- a/sdk/lib/_internal/pub/lib/src/source/hosted.dart
+++ b/sdk/lib/_internal/pub/lib/src/source/hosted.dart
@@ -71,7 +71,8 @@ class HostedSource extends Source {
       // a secondary cache of just pubspecs. This would let us have a
       // persistent cache for pubspecs for packages that haven't actually
       // been installed.
-      return new Pubspec.fromMap(version['pubspec'], systemCache.sources);
+      return new Pubspec.fromMap(version['pubspec'], systemCache.sources,
+          expectedName: id.name, location: url);
     }).catchError((ex) {
       var parsed = _parseDescription(id.description);
       _throwFriendlyError(ex, id, parsed.last);