dart2js cps: Maintain parent pointers instead of recomputing them.

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

Index: pkg/compiler/lib/src/cps_ir/share_interceptors.dart
diff --git a/pkg/compiler/lib/src/cps_ir/share_interceptors.dart b/pkg/compiler/lib/src/cps_ir/share_interceptors.dart
index 5ae912e81d0baa0b4698bff409c298eb1ecb024b..3706725e3d102a8c63b652ec7fe196761d9e435c 100644
--- a/pkg/compiler/lib/src/cps_ir/share_interceptors.dart
+++ b/pkg/compiler/lib/src/cps_ir/share_interceptors.dart
@@ -15,7 +15,7 @@ import '../constants/values.dart';
 ///- pull interceptors out of loops
 ///- replace interceptors with constants
 ///- share interceptors when one is in scope of the other
-class ShareInterceptors extends RecursiveVisitor implements Pass {
+class ShareInterceptors extends TrampolineRecursiveVisitor implements Pass {
   String get passName => 'Share interceptors';
 
   /// The innermost loop containing a given primitive.
@@ -115,6 +115,7 @@ class ShareInterceptors extends RecursiveVisitor implements Pass {
       // The interceptor could not be shared. Replace it with a constant.
       Constant constantPrim = new Constant(constant);
       node.primitive = constantPrim;
+      constantPrim.parent = node;
       constantPrim.hint = interceptor.hint;
       constantPrim.type = interceptor.type;
       constantPrim.substituteFor(interceptor);