Reapply "Separate out loop closure information."

pkg/compiler/lib/src/kernel/kernel_backend_strategy.dart

Index: pkg/compiler/lib/src/kernel/kernel_backend_strategy.dart
diff --git a/pkg/compiler/lib/src/kernel/kernel_backend_strategy.dart b/pkg/compiler/lib/src/kernel/kernel_backend_strategy.dart
index 771ff630eb6c3ef730d55d91ea228c023eb58957..4b8ff757640eeb5e6cc7b27f6c68e84a286177da 100644
--- a/pkg/compiler/lib/src/kernel/kernel_backend_strategy.dart
+++ b/pkg/compiler/lib/src/kernel/kernel_backend_strategy.dart
@@ -325,6 +325,12 @@ class KernelClosureClassMaps implements ClosureClassMaps<ir.Node> {
   ClosureAnalysisInfo getClosureAnalysisInfo(ir.Node node) {
     return const ClosureAnalysisInfo();
   }
+
+  @override
+  LoopClosureRepresentationInfo getClosureRepresentationInfoForLoop(
+      ir.Node loopNode) {
+    return const LoopClosureRepresentationInfo();
+  }
 }
 
 class KernelSorter implements Sorter {