Initial implementation of copy/paste support

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

+// 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:analysis_server/protocol/protocol_generated.dart';
+import 'package:analyzer/dart/ast/ast.dart';
+
+/**
+ * An object used to compute the list of elements referenced within a given
+ * region of a compilation unit that are imported into the compilation unit's
+ * library.
+ */
+class ImportedElementsComputer {
+  /**
+   * The compilation unit in which the elements are referenced.
+   */
+  final CompilationUnit unit;
+
+  /**
+   * The offset of the region containing the references to be returned.
+   */
+  final int offset;
+
+  /**
+   * The length of the region containing the references to be returned.
+   */
+  final int length;
+
+  /**
+   * Initialize a newly created computer to compute the list of imported
+   * elements referenced in the given [unit] within the region with the given
+   * [offset] and [length].
+   */
+  ImportedElementsComputer(this.unit, this.offset, this.length);
+
+  /**
+   * Compute and return the list of imported elements.
+   */
+  List<ImportedElements> compute() {
+    // TODO(brianwilkerson) Implement this.
+    return <ImportedElements>[];
+  }
+}