Use interceptors to handle runtime types.

dart/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart

Index: dart/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart b/dart/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
index e834e1ad84e7bdf703fdb28883b9ecb2873e3a0b..8c641b358eff6072d3f8ea24df3ef072cb3d607c 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
@@ -179,6 +179,12 @@ class JavaScriptBackend extends Backend {
   ClassElement jsPlainJavaScriptObjectClass;
   ClassElement jsUnknownJavaScriptObjectClass;
 
+  /// Class element for JsRuntimeType in interceptors.dart.
+  ClassElement jsRuntimeType;
+
+  /// Class element for JsFunctionType in interceptors.dart.
+  ClassElement jsFunctionType;
+
   ClassElement jsIndexableClass;
   ClassElement jsMutableIndexableClass;
 
@@ -513,6 +519,10 @@ class JavaScriptBackend extends Backend {
       jsUnknownJavaScriptObjectClass =
           compiler.findInterceptor(
               const SourceString('UnknownJavaScriptObject')),
+      jsRuntimeType =
+          compiler.findInterceptor(const SourceString('JsRuntimeType')),
+      jsFunctionType =
+          compiler.findInterceptor(const SourceString('JsFunctionType')),
     ];
 
     jsIndexableClass =
@@ -669,6 +679,10 @@ class JavaScriptBackend extends Backend {
       }
     }
 
+    // TODO(ahe): Find a better way to enable these interceptors.
+    addInterceptors(jsRuntimeType, enqueuer, elements);
+    addInterceptors(jsFunctionType, enqueuer, elements);
+
     // Register any helper that will be needed by the backend.
     if (enqueuer.isResolutionQueue) {
       if (cls == compiler.intClass