Refactor LoopHandler to avoid calling KernelAstAdapter.getNode

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 bf1f8b123daff1f36529a464adc6003b31a53346..df282f2a674e1002f201af6bb58895fbe9552779 100644
--- a/pkg/compiler/lib/src/kernel/kernel_backend_strategy.dart
+++ b/pkg/compiler/lib/src/kernel/kernel_backend_strategy.dart
@@ -277,6 +277,13 @@ class KernelToLocalsMapImpl implements KernelToLocalsMap {
       return new KLocal(node.name, currentMember);
     });
   }
+
+  @override
+  ClosureScope getClosureScopeForLoop(
+      ClosureClassMap closureData, ir.TreeNode node) {
+    // TODO(johnniwinther): Support closure scopes for loops.
+    return null;
+  }
 }
 
 class KLocal implements Local {