Implement JsKernelToElementMap through KernelToElementMapBase

pkg/compiler/lib/src/compiler.dart

Index: pkg/compiler/lib/src/compiler.dart
diff --git a/pkg/compiler/lib/src/compiler.dart b/pkg/compiler/lib/src/compiler.dart
index cbf31ba0454460799cf3eca6a406da17bc121cb4..50319f79b7dec97f43b5c5c75898692eba1112e3 100644
--- a/pkg/compiler/lib/src/compiler.dart
+++ b/pkg/compiler/lib/src/compiler.dart
@@ -636,8 +636,8 @@ abstract class Compiler {
   Enqueuer startCodegen(ClosedWorld closedWorld) {
     Enqueuer codegenEnqueuer = enqueuer.createCodegenEnqueuer(closedWorld);
     _codegenWorldBuilder = codegenEnqueuer.worldBuilder;
-    codegenEnqueuer
-        .applyImpact(backend.onCodegenStart(closedWorld, _codegenWorldBuilder));
+    codegenEnqueuer.applyImpact(backend.onCodegenStart(
+        closedWorld, _codegenWorldBuilder, backendStrategy.sorter));
     return codegenEnqueuer;
   }