Support patched generic methods.

pkg/compiler/lib/src/resolution/signatures.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart2js.resolution.signatures;
 
 import '../common.dart';
 import '../common/resolution.dart';
 import '../dart_types.dart';
 import '../elements/elements.dart';
@@ skipping 289 matching lines @@
       NodeList formalParameters,
       Node returnNode,
       FunctionTypedElement element,
       ResolutionRegistry registry,
       {MessageKind defaultValuesError,
       bool createRealParameters: false,
       bool isFunctionExpression: false}) {
     DiagnosticReporter reporter = resolution.reporter;
 
     List<DartType> createTypeVariables(NodeList typeVariableNodes) {
+      if (element.isPatch) {
+        FunctionTypedElement origin = element.origin;
+        origin.computeType(resolution);
+        return origin.typeVariables;
+      }
       if (typeVariableNodes == null) return const <DartType>[];
 
       // Create the types and elements corresponding to [typeVariableNodes].
       Link<Node> nodes = typeVariableNodes.nodes;
       List<DartType> arguments =
           new List.generate(nodes.slowLength(), (int index) {
         TypeVariable node = nodes.head;
         String variableName = node.name.source;
         nodes = nodes.tail;
         TypeVariableElementX variableElement =
@@ skipping 157 matching lines @@
 /// variables of the function signature itself when its signature is analyzed.
 class FunctionSignatureBuildingScope extends TypeVariablesScope {
   @override
   final List<DartType> typeVariables;
 
   FunctionSignatureBuildingScope(Scope parent, this.typeVariables)
       : super(parent);
 
   String toString() => 'FunctionSignatureBuildingScope($typeVariables)';
 }