dart2js cps: Introduce some built-in operators in type propagation.

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 '../dart2jslib.dart' as dart2js;
 import '../elements/elements.dart';
 import '../cps_ir/cps_ir_nodes.dart' as cps_ir;
 import '../util/util.dart' show CURRENT_ELEMENT_SPANNABLE;
@@ skipping 565 matching lines @@
     return continueWithExpression(node.continuation, value);
   }
 
   Statement visitSetStatic(cps_ir.SetStatic node) {
     SetStatic setStatic = new SetStatic(
         node.element,
         getVariableUse(node.value),
         node.sourceInformation);
     return new ExpressionStatement(setStatic, visit(node.body));
   }
+
+  Expression visitApplyBuiltinOperator(cps_ir.ApplyBuiltinOperator node) {
+    if (node.operator == BuiltinOperator.IsFalsy) {
+      return new Not(getVariableUse(node.arguments.single));
+    }
+    return new ApplyBuiltinOperator(node.operator,
+                                    translateArguments(node.arguments));
+  }
 }