Support runtime check of function types.

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

Index: sdk/lib/_internal/compiler/implementation/js_backend/runtime_types.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/runtime_types.dart b/sdk/lib/_internal/compiler/implementation/js_backend/runtime_types.dart
index e38cc6e4ec5cdfb227c73e01e26746629a831e3e..f400d3b6818c073f9d0757124b429ff442df34e0 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/runtime_types.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/runtime_types.dart
@@ -207,6 +207,25 @@ class RuntimeTypeInformation {
     }
   }
 
+  String getTypeEncoding(DartType type,
+                         {bool alwaysGenerateFunction: false}) {
+    TypeVariableType typeVariable = type.typeVariableOccurrence;
+    String onVariable(TypeVariableType v) {
+      return v.toString();
+    };
+    String encoding = _getTypeRepresentation(type, onVariable);
+    if (typeVariable == null && !alwaysGenerateFunction) {
+      return encoding;
+    } else {
+      ClassElement cls = typeVariable != null ?
+          typeVariable.element.enclosingElement : null;
+      String parameters = cls != null
+          ? cls.typeVariables.toList().join(', ')
+          : '';
+      return 'function ($parameters) { return $encoding; }';
+    }
+  }
+
   String getTypeRepresentation(DartType type, void onVariable(variable)) {
     // Create a type representation.  For type variables call the original
     // callback for side effects and return a template placeholder.