Add plugin support for occurrences (and fix typo)

pkg/analyzer_plugin/lib/src/utilities/occurrences/occurrences.dart

Index: pkg/analyzer_plugin/lib/src/utilities/occurrences/occurrences.dart
diff --git a/pkg/analyzer_plugin/lib/src/utilities/occurrences/occurrences.dart b/pkg/analyzer_plugin/lib/src/utilities/occurrences/occurrences.dart
new file mode 100644
index 0000000000000000000000000000000000000000..b88aa78955e633dea58eca09c21944dc32db0326
--- /dev/null
+++ b/pkg/analyzer_plugin/lib/src/utilities/occurrences/occurrences.dart
@@ -0,0 +1,60 @@
+// 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.
+
+import 'package:analyzer/dart/analysis/results.dart';
+import 'package:analyzer/file_system/file_system.dart';
+import 'package:analyzer_plugin/protocol/protocol_common.dart'
+    hide AnalysisError;
+import 'package:analyzer_plugin/utilities/occurrences/occurrences.dart';
+
+/**
+ * A concrete implementation of [DartOccurrencesRequest].
+ */
+class DartOccurrencesRequestImpl implements DartOccurrencesRequest {
+  @override
+  final ResourceProvider resourceProvider;
+
+  @override
+  final ResolveResult result;
+
+  /**
+   * Initialize a newly create request with the given data.
+   */
+  DartOccurrencesRequestImpl(this.resourceProvider, this.result);
+
+  @override
+  String get path => result.path;
+}
+
+/**
+ * A concrete implementation of [OccurrencesCollector].
+ */
+class OccurrencesCollectorImpl implements OccurrencesCollector {
+  /**
+   * The locations of the occurrences that have been collected.
+   */
+  Map<Element, List<int>> occurrenceLocations = <Element, List<int>>{};
+
+  /**
+   * Initialize a newly created collector.
+   */
+  OccurrencesCollectorImpl();
+
+  /**
+   * Return the list of occurrences that have been collected.
+   */
+  List<Occurrences> get occurrences {
+    List<Occurrences> occurrences = <Occurrences>[];
+    occurrenceLocations.forEach((Element element, List<int> offsets) {
+      offsets.sort();
+      occurrences.add(new Occurrences(element, offsets, element.name.length));
+    });
+    return occurrences;
+  }
+
+  @override
+  void addOccurrence(Element element, int offset) {
+    occurrenceLocations.putIfAbsent(element, () => <int>[]).add(offset);
+  }
+}