Remove JavaScriptBackend from ClosedWorldBase

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

Index: pkg/compiler/lib/src/ssa/codegen_helpers.dart
diff --git a/pkg/compiler/lib/src/ssa/codegen_helpers.dart b/pkg/compiler/lib/src/ssa/codegen_helpers.dart
index a554f18c6b10a0cceac78bc52df1bb7a3adc31d6..99d26797954e6c226a8e06508c1236790f34fd0a 100644
--- a/pkg/compiler/lib/src/ssa/codegen_helpers.dart
+++ b/pkg/compiler/lib/src/ssa/codegen_helpers.dart
@@ -142,7 +142,8 @@ class SsaInstructionSelection extends HBaseVisitor {
 
     if (interceptor.nonCheck() == receiverArgument.nonCheck()) {
       if (_interceptorData.isInterceptedSelector(selector) &&
-          !_interceptorData.isInterceptedMixinSelector(selector, mask)) {
+          !_interceptorData.isInterceptedMixinSelector(
+              selector, mask, _closedWorld)) {
         ConstantValue constant = new SyntheticConstantValue(
             SyntheticConstantKind.DUMMY_INTERCEPTOR,
             receiverArgument.instructionType);