fix #25183, add support to ErrorVerifier for generic methods

pkg/analyzer/lib/src/generated/type_system.dart

Index: pkg/analyzer/lib/src/generated/type_system.dart
diff --git a/pkg/analyzer/lib/src/generated/type_system.dart b/pkg/analyzer/lib/src/generated/type_system.dart
index f68e0317aa31697af4a226edb8419b711d6ef6fa..1da3b38572a2ece3bc26caad898bad81f172a839 100644
--- a/pkg/analyzer/lib/src/generated/type_system.dart
+++ b/pkg/analyzer/lib/src/generated/type_system.dart
@@ -566,6 +566,15 @@ abstract class TypeSystem {
       TypeProvider typeProvider, DartType type1, DartType type2);
 
   /**
+   * Given a [function] type, instantiate it with its bounds.
+   *
+   * The behavior of this method depends on the type system, for example, in
+   * classic Dart `dynamic` will be used for all type arguments, whereas
+   * strong mode prefers the actual bound type if it was specified.
+   */
+  FunctionType instantiateToBounds(FunctionType function);
+
+  /**
    * Return `true` if the [leftType] is assignable to the [rightType] (that is,
    * if leftType <==> rightType).
    */
@@ -673,6 +682,18 @@ class TypeSystemImpl implements TypeSystem {
     }
   }
 
+  /**
+   * Instantiate the function type using `dynamic` for all generic parameters.
+   */
+  FunctionType instantiateToBounds(FunctionType function) {
+    int count = function.boundTypeParameters.length;
+    if (count == 0) {
+      return function;
+    }
+    return function.instantiate(
+        new List<DartType>.filled(count, DynamicTypeImpl.instance));
+  }
+
   @override
   bool isAssignableTo(DartType leftType, DartType rightType) {
     return leftType.isAssignableTo(rightType);