fix #25409, error if a generic method argument did not have a corresponding parameter

pkg/analyzer/lib/src/task/strong/checker.dart

 // Copyright (c) 2015, 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.
 
 // TODO(jmesserly): this was ported from package:dev_compiler, and needs to be
 // refactored to fit into analyzer.
 library analyzer.src.task.strong.checker;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/dart/element/element.dart';
@@ skipping 111 matching lines @@
     checkAssignment(arg, expectedType);
   }
 
   void checkArgumentList(ArgumentList node, FunctionType type) {
     NodeList<Expression> list = node.arguments;
     int len = list.length;
     for (int i = 0; i < len; ++i) {
       Expression arg = list[i];
       ParameterElement element = arg.staticParameterElement;
       if (element == null) {
-        if (type.parameters.length < len) {
-          // We found an argument mismatch, the analyzer will report this too,
-          // so no need to insert an error for this here.
-          continue;
-        }
-        element = type.parameters[i];
-        // TODO(vsm): When can this happen?
-        assert(element != null);
+        // We found an argument mismatch, the analyzer will report this too,
+        // so no need to insert an error for this here.
+        continue;
       }
       DartType expectedType = _elementType(element);
       if (expectedType == null) expectedType = DynamicTypeImpl.instance;
       checkArgument(arg, expectedType);
     }
   }
 
   void checkAssignment(Expression expr, DartType type) {
     if (expr is ParenthesizedExpression) {
       checkAssignment(expr.expression, type);
@@ skipping 1092 matching lines @@
     } while (!current.isObject && !visited.contains(current));
   }
 
   void _recordMessage(StaticInfo info) {
     if (info == null) return;
     var error = info.toAnalysisError();
     if (error.errorCode.errorSeverity == ErrorSeverity.ERROR) _failure = true;
     _reporter.onError(error);
   }
 }