Add support for requesting units from resynthesizer.

pkg/analyzer/test/src/summary/resynthesize_test.dart

 // Copyright (c) 2015, 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 test.src.serialization.elements_test;
 
 import 'dart:convert';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
@@ skipping 2517 matching lines @@
   test_getElement_setter() {
     PropertyAccessorElement original =
         resolve2(addSource('class C { void set f(value) {} }'))
             .getType('C')
             .getSetter('f');
     expect(original, isNotNull);
     PropertyAccessorElement resynthesized = validateGetElement(original);
     comparePropertyAccessorElements(resynthesized, original, 'C.setter f');
   }
 
+  test_getElement_unit() {
+    Source source = addSource('class C { f() {} }');
+    CompilationUnitElement original = resolve2(source).definingCompilationUnit;
+    expect(original, isNotNull);
+    CompilationUnitElement resynthesized = validateGetElement(original);
+    compareCompilationUnitElements(resynthesized, original);
+  }
+
   test_getter_documented() {
     checkLibrary('''
 // Extra comment so doc comment offset != 0
 /**
  * Docs
  */
 get x => null;''');
   }
 
   test_getter_external() {
@@ skipping 862 matching lines @@
       fail('Unexpectedly tried to get unlinked summary for $uri');
     }
     return serializedUnit;
   }
 
   @override
   bool hasLibrarySummary(String uri) {
     return true;
   }
 }