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

pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library tree_ir_builder;
 
 import '../diagnostics/invariant.dart' show
     InternalErrorFunction;
 import '../diagnostics/spannable.dart' show
     CURRENT_ELEMENT_SPANNABLE;
@@ skipping 657 matching lines @@
                         getVariableUse(node.index),
                         getVariableUse(node.value));
   }
 
   @override
   NodeCallback visitAwait(cps_ir.Await node) {
     Expression value = new Await(getVariableUse(node.input));
     return makeCallExpression(node, value);
   }
 
+  @override
+  Expression visitRefinement(cps_ir.Refinement node) {
+    throw 'Unexpected Refinement node in tree builder';
+  }
+
   /********** UNUSED VISIT METHODS *************/
 
   unexpectedNode(cps_ir.Node node) {
     internalError(CURRENT_ELEMENT_SPANNABLE, 'Unexpected IR node: $node');
   }
 
   visitFunctionDefinition(cps_ir.FunctionDefinition node) {
     unexpectedNode(node);
   }
   visitParameter(cps_ir.Parameter node) => unexpectedNode(node);
   visitContinuation(cps_ir.Continuation node) => unexpectedNode(node);
   visitMutableVariable(cps_ir.MutableVariable node) => unexpectedNode(node);
 }