Split KernelToElementMap into sub-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 9aee8524ff1a0b3494c90ce388e7bf9177a79c49..8464fc551a620033c19b90e58291ac9582735d31 100644
--- a/tests/compiler/dart2js/kernel/impact_test.dart
+++ b/tests/compiler/dart2js/kernel/impact_test.dart
@@ -779,7 +779,7 @@ void checkLibrary(Compiler compiler, KernelToElementMapMixin elementMap,
 }
 
 void checkElement(
-    Compiler compiler, KernelToElementMapMixin elementMap, AstElement element,
+    Compiler compiler, KernelToElementMapImpl elementMap, AstElement element,
     {bool fullTest: false}) {
   if (!fullTest && element.library.isPlatformLibrary) {
     return;