Make some VM libraries patch cleanly using the analyzer.

sdk/lib/vmservice/asset.dart

Index: sdk/lib/vmservice/asset.dart
diff --git a/sdk/lib/vmservice/asset.dart b/sdk/lib/vmservice/asset.dart
index b8f6c207f94dd431d232f2c2f5c4d0fd617afb24..db0d97869b7fc59f73ad56dc7aac7ca884f2b2a4 100644
--- a/sdk/lib/vmservice/asset.dart
+++ b/sdk/lib/vmservice/asset.dart
@@ -38,23 +38,7 @@ class Asset {
   }
 
   /// Call to request assets from the embedder.
-  static HashMap<String, Asset> request() {
-    HashMap<String, Asset> assets = new HashMap<String, Asset>();
-    Uint8List tarBytes = _requestAssets();
-    if (tarBytes == null) {
-      return assets;
-    }
-    _TarArchive archive = new _TarArchive(tarBytes);
-    while (archive.hasNext()) {
-      Asset asset = archive.next();
-      if (asset == null) {
-        // Skip over special files.
-        continue;
-      }
-      assets[asset.name] = asset;
-    }
-    return assets;
-  }
+  external static HashMap<String, Asset> request();
 
   String toString() => '$name ($mimeType)';
 }