Add Class/MemberDefinition to handle synthesized classes/members

tests/compiler/dart2js/equivalence/id_equivalence_test.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 'dart:io';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/common.dart';
 import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/diagnostics/diagnostic_listener.dart';
 import 'package:compiler/src/elements/elements.dart';
@@ skipping 132 matching lines @@
 
 /// Compute a descriptive mapping of the [Id]s in [member] as a kernel based
 /// member.
 ///
 /// Fills [actualMap] with the data and [sourceSpanMap] with the source spans
 /// for the data origin.
 void computeIrMemberData(Compiler compiler, MemberEntity member,
     Map<Id, String> actualMap, Map<Id, Spannable> spannableMap) {
   KernelBackendStrategy backendStrategy = compiler.backendStrategy;
   KernelToElementMapForBuilding elementMap = backendStrategy.elementMap;
-  new IrComputer(actualMap, spannableMap).run(elementMap.getMemberNode(member));
+  MemberDefinition definition = elementMap.getMemberDefinition(member);
+  assert(definition.kind == MemberKind.regular,
+      failedAt(member, "Unexpected member definition $definition"));
+  new IrComputer(actualMap, spannableMap).run(definition.node);
 }
 
 /// IR visitor for computing a descriptive mapping of the [Id]s in a member.
 class IrComputer extends AbstractIrComputer with ComputerMixin {
   IrComputer(Map<Id, String> actualMap, Map<Id, SourceSpan> spannableMap)
       : super(actualMap, spannableMap);
 
   @override
   String computeNodeValue(ir.TreeNode node) {
     if (node is ir.VariableDeclaration) {
       return computeLocalName(node.name);
     } else if (node is ir.FunctionDeclaration) {
       return computeLocalName(node.variable.name);
     } else if (node is ir.MethodInvocation) {
       return computeDynamicInvokeName(node.name.name);
     } else if (node is ir.PropertyGet) {
       return computeDynamicGetName(node.name.name);
     }
     return '<unknown:$node>';
   }
 
   @override
   String computeMemberValue(ir.Member member) {
     return computeMemberName(member.enclosingClass?.name, member.name.name);
   }
 }