fix #27210, remove TypeParameterMember equality

pkg/analyzer/lib/src/dart/element/element.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 analyzer.src.dart.element.element;
 
 import 'dart:collection';
 import 'dart:math' show min;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 1512 matching lines @@
     List<FunctionElement> functions = this.functions;
     for (int i = 0; i < functions.length; i++) {
       if (functions[i].name == FunctionElement.LOAD_LIBRARY_NAME) {
         return true;
       }
     }
     return false;
   }
 
   @override
-  String get identifier => source.encoding;
+  String get identifier => source?.encoding;
 
   @override
   ElementKind get kind => ElementKind.COMPILATION_UNIT;
 
   @override
   List<ElementAnnotation> get metadata {
     if (_unlinkedPart != null) {
       return _metadata ??= _buildAnnotations(
           library.definingCompilationUnit as CompilationUnitElementImpl,
           _unlinkedPart.annotations);
@@ skipping 3954 matching lines @@
     }
     for (int i = 0; i < _parts.length; i++) {
       if (_parts[i].hasLoadLibraryFunction) {
         return true;
       }
     }
     return false;
   }
 
   @override
-  String get identifier => _definingCompilationUnit.source.encoding;
+  String get identifier => _definingCompilationUnit.source?.encoding;
 
   @override
   List<LibraryElement> get importedLibraries {
     HashSet<LibraryElement> libraries = new HashSet<LibraryElement>();
     for (ImportElement element in imports) {
       LibraryElement library = element.importedLibrary;
       if (library != null) {
         libraries.add(library);
       }
     }
@@ skipping 2926 matching lines @@
 
   @override
   void visitElement(Element element) {
     int offset = element.nameOffset;
     if (offset != -1) {
       map[offset] = element;
     }
     super.visitElement(element);
   }
 }