Remove backend dependency from TypeTestRegistry

pkg/compiler/lib/src/js_backend/runtime_types.dart

Index: pkg/compiler/lib/src/js_backend/runtime_types.dart
diff --git a/pkg/compiler/lib/src/js_backend/runtime_types.dart b/pkg/compiler/lib/src/js_backend/runtime_types.dart
index 5a8f41c2044b028de51d406e75ec6966b97becea..a9cf0ba1cb6b664cdf264d4369b61a57d169700a 100644
--- a/pkg/compiler/lib/src/js_backend/runtime_types.dart
+++ b/pkg/compiler/lib/src/js_backend/runtime_types.dart
@@ -435,6 +435,8 @@ class _RuntimeTypes extends _RuntimeTypesBase
 
   JavaScriptBackend get backend => compiler.backend;
 
+  bool rtiChecksBuilderClosed = false;
+
   _RuntimeTypes(Compiler compiler)
       : this.compiler = compiler,
         checkedTypeArguments = new Set<ResolutionDartType>(),
@@ -487,6 +489,7 @@ class _RuntimeTypes extends _RuntimeTypesBase
     computeCheckedArguments(instantiatedTypesAndClosures, isChecks);
     cachedRequiredChecks =
         computeChecks(allInstantiatedArguments, checkedArguments);
+    rtiChecksBuilderClosed = true;
     return new _RuntimeTypesChecks(this, cachedRequiredChecks,
         directlyInstantiatedArguments, checkedArguments);
   }