AnalysisDriver.getUnitElement() should return a structure with a key.

pkg/analyzer/test/src/dart/analysis/driver_test.dart

 // Copyright (c) 2016, 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 analyzer.test.driver;
 
 import 'dart:async';
 import 'dart:convert';
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 1522 matching lines @@
 
   test_getUnitElement() async {
     String content = r'''
 foo(int p) {}
 main() {
   foo(42);
 }
 ''';
     addTestFile(content);
 
-    CompilationUnitElement unitElement = await driver.getUnitElement(testFile);
-    expect(unitElement, isNotNull);
+    UnitElementResult unitResult = await driver.getUnitElement(testFile);
+    expect(unitResult, isNotNull);
+    CompilationUnitElement unitElement = unitResult.element;
     expect(unitElement.source.fullName, testFile);
     expect(unitElement.functions.map((c) => c.name),
         unorderedEquals(['foo', 'main']));
   }
 
   test_getUnitElement_notDart() async {
     var path = _p('/test.txt');
     provider.newFile(path, 'class A {}');
-    CompilationUnitElement unit = await driver.getUnitElement(path);
-    expect(unit, isNotNull);
-    expect(unit.types.map((e) => e.name), ['A']);
+    UnitElementResult unitResult = await driver.getUnitElement(path);
+    expect(unitResult, isNotNull);
+    expect(unitResult.element.types.map((e) => e.name), ['A']);
   }
 
   test_hasFilesToAnalyze() async {
     // No files yet, nothing to analyze.
     expect(driver.hasFilesToAnalyze, isFalse);
 
     // Add a new file, it should be analyzed.
     addTestFile('main() {}', priority: false);
     expect(driver.hasFilesToAnalyze, isTrue);
 
@@ skipping 769 matching lines @@
    * Return the [provider] specific path for the given Posix [path].
    */
   String _p(String path) => provider.convertPath(path);
 
   static String _md5(String content) {
     return hex.encode(md5.convert(UTF8.encode(content)).bytes);
   }
 }
 
 class _SourceMock extends TypedMock implements Source {}