dart2js cps: Use definitions by default, not references.

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

 library dart2js.cps_ir.update_refinements;
 
 import 'cps_ir_nodes.dart';
 import 'optimizers.dart' show Pass;
 import 'type_mask_system.dart';
 import '../world.dart';
 
 /// Updates all references to use the most refined version in scope.
 ///
 /// [GVN] and [RedundantJoinElimination], and possibly other passes, can create
@@ skipping 19 matching lines @@
     visit(node);
   }
 
   Expression traverseLetPrim(LetPrim node) {
     Expression next = node.body;
     visit(node.primitive);
     return next;
   }
 
   visitReceiverCheck(ReceiverCheck node) {
-    if (refine(node.value)) {
+    if (refine(node.valueRef)) {
       // Update the type if the input has changed.
-      Primitive value = node.value.definition;
+      Primitive value = node.value;
       if (value.type.needsNoSuchMethodHandling(node.selector, classWorld)) {
         node.type = typeSystem.receiverTypeFor(node.selector, value.type);
       } else {
         // Check is no longer needed.
         node..replaceUsesWith(value)..destroy();
         LetPrim letPrim = node.parent;
         letPrim.remove();
         return;
       }
     }
@@ skipping 16 matching lines @@
     Primitive old = refinementFor[value];
     refinementFor[value] = node;
     pushAction(() {
       refinementFor[value] = old;
     });
   }
 
   visitBoundsCheck(BoundsCheck node) {
     super.visitBoundsCheck(node);
     if (node.hasIntegerCheck &&
-        typeSystem.isDefinitelyInt(node.index.definition.type)) {
+        typeSystem.isDefinitelyInt(node.index.type)) {
       node.checks &= ~BoundsCheck.INTEGER;
     }
   }
 
   processReference(Reference ref) {
     refine(ref);
   }
 
   bool refine(Reference ref) {
     Definition def = ref.definition;
     if (def is Primitive) {
       Primitive refinement = refinementFor[def.effectiveDefinition];
       if (refinement != null && refinement != ref.definition) {
         ref.changeTo(refinement);
         return true;
       }
     }
     return false;
   }
 }