Split KernelToElementMap into sub-interfaces

tests/compiler/dart2js/kernel/compile_from_dill_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.
 
 // Partial test that the closed world computed from [WorldImpact]s derived from
 // kernel is equivalent to the original computed from resolution.
 library dart2js.kernel.compile_from_dill_test;
 
 import 'dart:async';
 import 'dart:io';
@@ skipping 124 matching lines @@
       const {},
       [
         Flags.disableTypeInference,
         Flags.disableInlining,
         Flags.enableAssertMessage
       ],
       printSteps: true,
       compilerOutput: collector2);
 
   KernelFrontEndStrategy frontendStrategy = compiler2.frontendStrategy;
-  KernelToElementMap elementMap = frontendStrategy.elementMap;
+  KernelToElementMapForBuilding elementMap = frontendStrategy.elementMap;
 
   Expect.isFalse(compiler2.compilationFailed);
 
   KernelEquivalence equivalence = new KernelEquivalence(elementMap);
 
   ClosedWorld closedWorld2 =
       compiler2.resolutionWorldBuilder.closedWorldForTesting;
 
   checkBackendUsage(closedWorld1.backendUsage, closedWorld2.backendUsage,
       equivalence.defaultStrategy);
@@ skipping 45 matching lines @@
     }
     Map<String, BufferedOutputSink> map2 = collector2.outputMap[outputType];
     checkSets(map1.keys, map2.keys, 'output', equality);
     map1.forEach((String name, BufferedOutputSink output1) {
       BufferedOutputSink output2 = map2[name];
       Expect.stringEquals(output1.text, output2.text);
     });
   });
   return ResultKind.success;
 }