Extract CallStructure from Selector.

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

Index: pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart
index fee4b77d92539de4c368501b8077f3b1da952063..b3632d131f789157b2a38a3f03a635a8bb7edec3 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart
@@ -501,11 +501,9 @@ abstract class IrBuilder {
   }
 
   ir.Primitive _buildInvokeCall(ir.Primitive target,
-                                 Selector selector,
-                                 List<ir.Definition> arguments) {
-    Selector callSelector = new Selector.callClosure(
-        selector.argumentCount,
-        selector.namedArguments);
+                                Selector selector,
+                                List<ir.Definition> arguments) {
+    Selector callSelector = new Selector.callClosureFrom(selector);
     return _buildInvokeDynamic(target, callSelector, arguments);
   }