Split KernelToElementMap into sub-interfaces

tests/compiler/dart2js/kernel/impact_test.dart

 // Copyright (c) 2016, 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.kernel.impact_test;
 
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/commandline_options.dart';
 import 'package:compiler/src/common.dart';
 import 'package:compiler/src/common/names.dart';
@@ skipping 761 matching lines @@
       });
     } else if (element.isTypedef) {
       // Skip typedefs.
     } else {
       checkElement(compiler, elementMap, element, fullTest: fullTest);
     }
   });
 }
 
 void checkElement(
-    Compiler compiler, KernelToElementMapMixin elementMap, AstElement element,
+    Compiler compiler, KernelToElementMapImpl elementMap, AstElement element,
     {bool fullTest: false}) {
   if (!fullTest && element.library.isPlatformLibrary) {
     return;
   }
   if (element.isConstructor) {
     ConstructorElement constructor = element;
     if (constructor.isRedirectingFactory) {
       // Skip redirecting constructors for now; they might not be supported.
       return;
     }
@@ skipping 109 matching lines @@
         builder.registerFeature(Feature.THROW_EXPRESSION);
         break;
       default:
         builder.registerFeature(feature);
         break;
     }
   }
   impact.nativeData.forEach(builder.registerNativeData);
   return builder;
 }