Don't crash when tree shaking is disabled

pkg/compiler/lib/src/resolution/class_members.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.
 
 library dart2js.resolution.compute_members;
 
 import '../common.dart';
 import '../common/names.dart' show Identifiers, Names;
 import '../common/resolution.dart' show Resolution;
 import '../compiler.dart' show Compiler;
@@ skipping 858 matching lines @@
             classMembers, interfaceMembers);
   }
 
   static Iterable<String> _EMPTY_MEMBERS_NAMES = const <String>[];
 
   /// Compute the members by the name [name] for this class. [names] collects
   /// the set of possible variations of [name], including getter, setter and
   /// and private names.
   void computeClassMember(
       Resolution resolution, String name, Setlet<Name> names) {
+    // TODO(johnniwinther): Should we assert that the class has been resolved
+    // instead?
+    ensureResolved(resolution);
     if (isMemberComputed(name)) return;
     if (Name.isPrivateName(name)) {
       names
         ..add(new Name(name, library))
         ..add(new Name(name, library, isSetter: true));
     }
     MembersCreator creator = _prepareCreator(resolution);
     creator.computeMembersByName(name, names);
     if (computedMemberNames == null) {
       computedMemberNames = _EMPTY_MEMBERS_NAMES;
     }
     if (name != Identifiers.call) {
       Setlet<String> set;
       if (identical(computedMemberNames, _EMPTY_MEMBERS_NAMES)) {
         computedMemberNames = set = new Setlet<String>();
       } else {
         set = computedMemberNames;
       }
       set.add(name);
     }
   }
 
   void computeAllClassMembers(Resolution resolution) {
+    // TODO(johnniwinther): Should we assert that the class has been resolved
+    // instead?
+    ensureResolved(resolution);
     if (areAllMembersComputed()) return;
     MembersCreator creator = _prepareCreator(resolution);
     creator.computeAllMembers();
     computedMemberNames = null;
     assert(invariant(this, areAllMembersComputed()));
   }
 
   bool areAllMembersComputed() {
     return computedMemberNames == null && classMembers != null;
   }
@@ skipping 34 matching lines @@
         message: "Members have not been fully computed for $this."));
     if (interfaceMembersAreClassMembers) {
       classMembers.forEach((_, member) {
         if (!member.isStatic) f(member);
       });
     } else {
       interfaceMembers.forEach((_, member) => f(member));
     }
   }
 }