Add observatory_pub_packages snapshot to third_party

observatory_pub_packages/analyzer/src/generated/interner.dart

Index: observatory_pub_packages/analyzer/src/generated/interner.dart
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--- observatory_pub_packages/analyzer/src/generated/interner.dart	(revision 0)
+++ observatory_pub_packages/analyzer/src/generated/interner.dart	(working copy)
@@ -0,0 +1,49 @@
+// 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 interner;
+
+import 'dart:collection';
+
+/**
+ * The interface `Interner` defines the behavior of objects that can intern
+ * strings.
+ */
+abstract class Interner {
+  /**
+   * Return a string that is identical to all of the other strings that have
+   * been interned that are equal to the given [string].
+   */
+  String intern(String string);
+}
+
+/**
+ * The class `MappedInterner` implements an interner that uses a map to manage
+ * the strings that have been interned.
+ */
+class MappedInterner implements Interner {
+  /**
+   * A table mapping strings to themselves.
+   */
+  Map<String, String> _table = new HashMap<String, String>();
+
+  @override
+  String intern(String string) {
+    String original = _table[string];
+    if (original == null) {
+      _table[string] = string;
+      return string;
+    }
+    return original;
+  }
+}
+
+/**
+ * The class `NullInterner` implements an interner that does nothing (does not
+ * actually intern any strings).
+ */
+class NullInterner implements Interner {
+  @override
+  String intern(String string) => string;
+}