Replace try/finally with PerformanceTag.makeCurrentWhile().

pkg/analyzer/lib/src/generated/source_io.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.source.io;
 
 import 'engine.dart';
@@ skipping 111 matching lines @@
   /**
    * Initialize a newly created source object.
    *
    * @param file the file represented by this source
    * @param uri the URI from which this source was originally derived
    */
   FileBasedSource.con2(this.uri, this.file);
 
   @override
   TimestampedData<String> get contents {
-    PerformanceTag prevTag = PerformanceStatistics.io.makeCurrent();
-    try {
+    return PerformanceStatistics.io.makeCurrentWhile(() {
       return contentsFromFile;
-    } finally {
-      prevTag.makeCurrent();
-    }
+    });
   }
 
   /**
    * Get the contents and timestamp of the underlying file.
    *
    * Clients should consider using the the method [AnalysisContext.getContents]
    * because contexts can have local overrides of the content of a source that the source is not
    * aware of.
    *
    * @return the contents of the source paired with the modification stamp of the source
@@ skipping 373 matching lines @@
   }
 
   /**
    * Return `true` if the given URI is a `file` URI.
    *
    * @param uri the URI being tested
    * @return `true` if the given URI is a `file` URI
    */
   static bool isFileUri(Uri uri) => uri.scheme == FILE_SCHEME;
 }