Instrumentation support

pkg/analyzer/lib/instrumentation/instrumentation.dart

Index: pkg/analyzer/lib/instrumentation/instrumentation.dart
diff --git a/pkg/analyzer/lib/instrumentation/instrumentation.dart b/pkg/analyzer/lib/instrumentation/instrumentation.dart
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+// 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.
+
+library instrumentation;
+
+/**
+ * The interface used by client code to communicate with an instrumentation
+ * server.
+ */
+abstract class InstrumentationServer {
+  /**
+   * Pass the given [message] to the instrumentation server so that it will be
+   * logged with other messages.
+   */
+  void log(String message);
+
+  /**
+   * Signal that the client is done communicating with the instrumentation
+   * server. This method should be invoked exactly one time and no other methods
+   * should be invoked on this instance after this method has been invoked.
+   */
+  void shutdown();
+}
+
+/**
+ * An [InstrumentationServer] that ignores all instrumentation requests sent to
+ * it. It can be used when no instrumentation data is to be collected as a way
+ * to avoid needing to check for null values.
+ */
+class NullInstrumentationServer implements InstrumentationServer {
+  /**
+   * Initialize a newly created instance of this class.
+   */
+  const NullInstrumentationServer();
+
+  @override
+  void log(String message) {
+  }
+
+  @override
+  void shutdown() {
+  }
+}