Extract interceptor calls from raw is-checks.

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

Index: sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
index 7a809b704837a6196034428490b1419483c962a2..6bf39b4bc3d3749b1b4c4b0a2856ee5263d9368e 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
@@ -1284,6 +1284,23 @@ class JavaScriptBackend extends Backend {
     }
   }
 
+  /**
+   * Returns [:true:] if the checking of [type] is performed directly on the
+   * object and not on an interceptor.
+   */
+  bool hasDirectCheckFor(DartType type) {
+    Element element = type.element;
+    return element == compiler.stringClass ||
+        element == compiler.boolClass ||
+        element == compiler.numClass ||
+        element == compiler.intClass ||
+        element == compiler.doubleClass ||
+        element == jsArrayClass ||
+        element == jsMutableArrayClass ||
+        element == jsExtendableArrayClass ||
+        element == jsFixedArrayClass;
+  }
+
   Element getExceptionUnwrapper() {
     return compiler.findHelper(const SourceString('unwrapException'));
   }