Replace try/finally with PerformanceTag.makeCurrentWhile().

pkg/analyzer/lib/src/services/lint.dart

 // Copyright (c) 2015, 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.
 
 library lint;
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/utilities_general.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/error.dart';
@@ skipping 24 matching lines @@
 
   final Iterable<CompilationUnit> _compilationUnits;
   final AnalysisErrorListener _errorListener;
   final Iterable<Linter> _linters;
 
   LintGenerator(this._compilationUnits, this._errorListener,
       [Iterable<Linter> linters])
       : _linters = linters != null ? linters : LINTERS;
 
   void generate() {
-    PerformanceTag prevTag = PerformanceStatistics.lint.makeCurrent();
-    try {
+    PerformanceStatistics.lint.makeCurrentWhile(() {
       _compilationUnits.forEach((cu) {
         if (cu.element != null) {
           _generate(cu, cu.element.source);
         }
       });
-    } finally {
-      prevTag.makeCurrent();
-    }
+    });
   }
 
   void _generate(CompilationUnit unit, Source source) {
     ErrorReporter errorReporter = new ErrorReporter(_errorListener, source);
     _linters.forEach((l) => l.reporter = errorReporter);
     Iterable<AstVisitor> visitors = _linters.map((l) => l.getVisitor());
     unit.accept(new DelegatingAstVisitor(visitors.where((v) => v != null)));
   }
 }