dart2js cps: Do not propagate impure expressions across null receiver.

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 '../dart_types.dart';
 import '../elements/elements.dart';
 import '../cps_ir/cps_ir_nodes.dart' as cps_ir;
@@ skipping 332 matching lines @@
 
   Statement visitInvokeStatic(cps_ir.InvokeStatic node) {
     // Calls are translated to direct style.
     List<Expression> arguments = translateArguments(node.arguments);
     Expression invoke = new InvokeStatic(node.target, node.selector, arguments,
         sourceInformation: node.sourceInformation);
     return continueWithExpression(node.continuation, invoke);
   }
 
   Statement visitInvokeMethod(cps_ir.InvokeMethod node) {
-    Expression invoke = new InvokeMethod(getVariableUse(node.receiver),
-                                         node.selector,
-                                         translateArguments(node.arguments));
+    InvokeMethod invoke = new InvokeMethod(getVariableUse(node.receiver),
+                                           node.selector,
+                                           translateArguments(node.arguments));
+    invoke.receiverIsNotNull = node.receiverIsNotNull;
     return continueWithExpression(node.continuation, invoke);
   }
 
   Statement visitInvokeMethodDirectly(cps_ir.InvokeMethodDirectly node) {
     Expression receiver = getVariableUse(node.receiver);
     List<Expression> arguments = translateArguments(node.arguments);
     Expression invoke = new InvokeMethodDirectly(receiver, node.target,
         node.selector, arguments);
     return continueWithExpression(node.continuation, invoke);
   }
@@ skipping 205 matching lines @@
 
   Statement visitSetStatic(cps_ir.SetStatic node) {
     SetStatic setStatic = new SetStatic(
         node.element,
         getVariableUse(node.value),
         node.sourceInformation);
     return new ExpressionStatement(setStatic, visit(node.body));
   }
 }