Add OCCURRENCES_CONTRIBUTOR_EXTENSION_POINT_ID.

pkg/analysis_server/lib/src/computer/computer_occurrences.dart

-// 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 computer.occurrences;
-
-import 'dart:collection';
-
-import 'package:analysis_server/src/protocol_server.dart' as protocol;
-import 'package:analyzer/src/generated/ast.dart';
-import 'package:analyzer/src/generated/element.dart';
-
-/**
- * A computer for elements occurrences in a Dart [CompilationUnit].
- */
-class DartUnitOccurrencesComputer {
-  final CompilationUnit _unit;
-
-  final Map<Element, List<int>> _elementsOffsets =
-      new HashMap<Element, List<int>>();
-
-  DartUnitOccurrencesComputer(this._unit);
-
-  /**
-   * Returns the computed occurrences, not `null`.
-   */
-  List<protocol.Occurrences> compute() {
-    _unit.accept(new _DartUnitOccurrencesComputerVisitor(this));
-    List<protocol.Occurrences> occurrences = <protocol.Occurrences>[];
-    _elementsOffsets.forEach((engineElement, offsets) {
-      var serverElement = protocol.newElement_fromEngine(engineElement);
-      var length = engineElement.displayName.length;
-      occurrences.add(new protocol.Occurrences(serverElement, offsets, length));
-    });
-    return occurrences;
-  }
-
-  void _addOccurrence(Element element, int offset) {
-    element = _canonicalizeElement(element);
-    if (element == null || element == DynamicElementImpl.instance) {
-      return;
-    }
-    List<int> offsets = _elementsOffsets[element];
-    if (offsets == null) {
-      offsets = <int>[];
-      _elementsOffsets[element] = offsets;
-    }
-    offsets.add(offset);
-  }
-
-  Element _canonicalizeElement(Element element) {
-    if (element is FieldFormalParameterElement) {
-      element = (element as FieldFormalParameterElement).field;
-    }
-    if (element is PropertyAccessorElement) {
-      element = (element as PropertyAccessorElement).variable;
-    }
-    if (element is Member) {
-      element = (element as Member).baseElement;
-    }
-    return element;
-  }
-}
-
-class _DartUnitOccurrencesComputerVisitor extends RecursiveAstVisitor {
-  final DartUnitOccurrencesComputer computer;
-
-  _DartUnitOccurrencesComputerVisitor(this.computer);
-
-  @override
-  visitSimpleIdentifier(SimpleIdentifier node) {
-    Element element = node.bestElement;
-    if (element != null) {
-      computer._addOccurrence(element, node.offset);
-    }
-    return super.visitSimpleIdentifier(node);
-  }
-}