dart2js cps: Add path-sensitive types by inserting refinement IR nodes.

pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart

Index: pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart
diff --git a/pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart b/pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart
index 011af0f5fbbb442a661bdf39b016b513c5a40a9e..0e617829efa8fe0dbd6082ebf985f30437f25934 100644
--- a/pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart
+++ b/pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart
@@ -693,6 +693,10 @@ class ParentVisitor extends RecursiveVisitor {
     node.continuation.parent = node;
     node.input.parent = node;
   }
+
+  processRefinement(Refinement node) {
+    node.value.parent = node;
+  }
 }
 
 class _ReductionKind {