Use native async/await support in pub.

sdk/lib/_internal/pub/test/test_pub.dart

Index: sdk/lib/_internal/pub/test/test_pub.dart
diff --git a/sdk/lib/_internal/pub/test/test_pub.dart b/sdk/lib/_internal/pub/test/test_pub.dart
index 4b6afb3408f609d2bcc10b76a04768b1eed85dc6..cb555a085dcc4f7dd484efd02c065b5c66f84928 100644
--- a/sdk/lib/_internal/pub/test/test_pub.dart
+++ b/sdk/lib/_internal/pub/test/test_pub.dart
@@ -809,16 +809,8 @@ Map packageMap(String name, String version, [Map dependencies]) {
 }
 
 /// Resolves [target] relative to the path to pub's `test/asset` directory.
-String testAssetPath(String target) {
-  var libPath = libraryPath('test_pub');
-
-  // We are running from the generated directory, but non-dart assets are only
-  // in the canonical directory.
-  // TODO(rnystrom): Remove this when #104 is fixed.
-  libPath = libPath.replaceAll('pub_generated', 'pub');
-
-  return p.join(p.dirname(libPath), 'asset', target);
-}
+String testAssetPath(String target) =>
+    p.join(p.dirname(libraryPath('test_pub')), 'asset', target);
 
 /// Returns a Map in the format used by the pub.dartlang.org API to represent a
 /// package version.