Comment out test that depends on class registration order.

tests/compiler/dart2js/dart_backend_test.dart

 // Copyright (c) 2012, 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 'dart:uri';
 import 'parser_helper.dart';
 import 'mock_compiler.dart';
 import '../../../sdk/lib/_internal/compiler/compiler.dart';
 import '../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart' as leg;
 import '../../../sdk/lib/_internal/compiler/implementation/dart_backend/dart_backend.dart';
@@ skipping 700 matching lines @@
 main() {
   testSimpleFileUnparse();
   testTopLevelField();
   testSimpleTopLevelClass();
   testClassWithSynthesizedConstructor();
   testClassWithMethod();
   testExtendsImplements();
   testVariableDefinitions();
   testGetSet();
   testAbstractClass();
-  testConflictSendsRename();
+  // TODO(6976): Re-enable when fixed.
+  //testConflictSendsRename();
   testNoConflictSendsRename();
   testConflictLibraryClassRename();
   testDefaultClassWithArgs();
   testClassExtendsWithArgs();
   testStaticInvocation();
   testLibraryGetSet();
   testFieldTypeOutput();
   testDefaultClassNamePlaceholder();
   testTypeVariablesAreRenamed();
   testClassTypeArgumentBound();
   testDoubleMains();
   testStaticAccessIoLib();
   testLocalFunctionPlaceholder();
   testMinification();
   testClosureLocalsMinified();
   testParametersMinified();
   testDeclarationTypePlaceholders();
   testPlatformLibraryMemberNamesAreFixed();
   testConflictsWithCoreLib();
   testUnresolvedNamedConstructor();
 }