dart2js cps: Support --trust-primitives and --trust-type-annotations.

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 3f69cd04c4958acf26b6e392babe5c9f61ab47bb..e6235913154d9fc866733d22a81aceaaff190f35 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart
@@ -2813,6 +2813,10 @@ class IrBuilder {
       return new ir.Yield(value, hasStar, k);
     });
   }
+
+  ir.Primitive buildRefinement(ir.Primitive value, TypeMask type) {
+    return addPrimitive(new ir.Refinement(value, type));
+  }
 }
 
 /// Location of a variable relative to a given closure.