Split KernelToElementMap mixins to match interfaces

tests/compiler/dart2js/kernel/impact_test.dart

Index: tests/compiler/dart2js/kernel/impact_test.dart
diff --git a/tests/compiler/dart2js/kernel/impact_test.dart b/tests/compiler/dart2js/kernel/impact_test.dart
index 8464fc551a620033c19b90e58291ac9582735d31..f0ce94dc838580821c22ffc53be8c312116d4cdf 100644
--- a/tests/compiler/dart2js/kernel/impact_test.dart
+++ b/tests/compiler/dart2js/kernel/impact_test.dart
@@ -15,7 +15,6 @@ import 'package:compiler/src/elements/elements.dart';
 import 'package:compiler/src/elements/entities.dart';
 import 'package:compiler/src/elements/resolution_types.dart';
 import 'package:compiler/src/js_backend/backend.dart';
-import 'package:compiler/src/kernel/element_map.dart';
 import 'package:compiler/src/kernel/element_map_impl.dart';
 import 'package:compiler/src/resolution/registry.dart';
 import 'package:compiler/src/resolution/tree_elements.dart';
@@ -759,7 +758,7 @@ main(List<String> args) {
   });
 }
 
-void checkLibrary(Compiler compiler, KernelToElementMapMixin elementMap,
+void checkLibrary(Compiler compiler, KernelToElementMapImpl elementMap,
     LibraryElement library,
     {bool fullTest: false}) {
   library.forEachLocalMember((_element) {