Extract InterceptorData from JavaScriptBackend.

pkg/compiler/lib/src/js_emitter/native_emitter.dart

Index: pkg/compiler/lib/src/js_emitter/native_emitter.dart
diff --git a/pkg/compiler/lib/src/js_emitter/native_emitter.dart b/pkg/compiler/lib/src/js_emitter/native_emitter.dart
index c49895a6612ec1a54f07eaadf687c6f375efd6b3..ef26ac69db0bb678d0bcd3a86bd0ac239141f1a5 100644
--- a/pkg/compiler/lib/src/js_emitter/native_emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/native_emitter.dart
@@ -346,7 +346,8 @@ class NativeEmitter {
   }
 
   bool isSupertypeOfNativeClass(ClassEntity element) {
-    if (backend.classesMixedIntoInterceptedClasses.contains(element)) {
+    if (backend.interceptorData.classesMixedIntoInterceptedClasses
+        .contains(element)) {
       return true;
     }
 
@@ -361,7 +362,7 @@ class NativeEmitter {
     // the type info.  i.e the criteria for whether or not to use an interceptor
     // is whether the receiver can be native, not the type of the test.
     ClassEntity cls = element;
-    if (backend.isNativeOrExtendsNative(cls)) return true;
+    if (backend.nativeData.isNativeOrExtendsNative(cls)) return true;
     return isSupertypeOfNativeClass(element);
   }
 }