Refactor and simplify the dart2dart renamer.

sdk/lib/_internal/compiler/implementation/cps_ir/cps_ir_builder.dart

Index: sdk/lib/_internal/compiler/implementation/cps_ir/cps_ir_builder.dart
diff --git a/sdk/lib/_internal/compiler/implementation/cps_ir/cps_ir_builder.dart b/sdk/lib/_internal/compiler/implementation/cps_ir/cps_ir_builder.dart
index 21c0349ccd99ff757af78c668244617f047fe549..40ad86170e1378710fd31afe22d35d076495d71d 100644
--- a/sdk/lib/_internal/compiler/implementation/cps_ir/cps_ir_builder.dart
+++ b/sdk/lib/_internal/compiler/implementation/cps_ir/cps_ir_builder.dart
@@ -110,6 +110,10 @@ class IrBuilderTask extends CompilerTask {
     if (function is ConstructorElement && function.isRedirectingFactory) {
       return false;
     }
+    // TODO(kmillikin,sigurdm): support syntax for factory constructors
+    if (function is ConstructorElement && function.isFactoryConstructor) {
+      return false;
+    }
 
     return true;
   }