Reduce use of Compiler.closedWorld

pkg/compiler/lib/src/native/ssa.dart

Index: pkg/compiler/lib/src/native/ssa.dart
diff --git a/pkg/compiler/lib/src/native/ssa.dart b/pkg/compiler/lib/src/native/ssa.dart
index f3134c37ed3aaddd9f07ab945a301b0e41c7f9bb..945995d2f63a324221619416199794c15689a7bd 100644
--- a/pkg/compiler/lib/src/native/ssa.dart
+++ b/pkg/compiler/lib/src/native/ssa.dart
@@ -101,7 +101,7 @@ void handleSsaNative(SsaBuilder builder, Expression nativeBody) {
         // be proportional to the number of native methods, which is bounded
         // by the dart: libraries.
         js.js.uncachedExpressionTemplate(nativeMethodCall),
-        backend.dynamicType,
+        builder.commonMasks.dynamicType,
         inputs,
         effects: new SideEffects()));
     // TODO(johnniwinther): Provide source information.
@@ -122,6 +122,6 @@ void handleSsaNative(SsaBuilder builder, Expression nativeBody) {
         <HInstruction>[],
         new SideEffects(),
         null,
-        backend.dynamicType));
+        builder.commonMasks.dynamicType));
   }
 }