Eliminate dependencies on pkg/front_end.

pkg/analyzer/lib/src/dart/analysis/performance_logger.dart

Index: pkg/analyzer/lib/src/dart/analysis/performance_logger.dart
diff --git a/pkg/analyzer/lib/src/dart/analysis/performance_logger.dart b/pkg/analyzer/lib/src/dart/analysis/performance_logger.dart
new file mode 100644
index 0000000000000000000000000000000000000000..2fd3ee1992c25a9fbeeb63f63794825119fd1160
--- /dev/null
+++ b/pkg/analyzer/lib/src/dart/analysis/performance_logger.dart
@@ -0,0 +1,8 @@
+// Copyright (c) 2017, 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 library re-exports the parts of front_end's performance_logger.dart
+// whose API is stable enough to be relied upon by clients.
+
+export 'package:front_end/src/base/performace_logger.dart' show PerformanceLog;