fix missing `bool` type annotation on dynamicIsBottom

pkg/analyzer/lib/src/generated/type_system.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.
 
 library analyzer.src.generated.type_system;
 
 import 'dart:collection';
 import 'dart:math' as math;
 
 import 'package:analyzer/dart/ast/token.dart' show TokenType;
@@ skipping 889 matching lines @@
    * we don't know what function value will be passed there.
    */
   FunctionType functionTypeToConcreteType(
       TypeProvider typeProvider, FunctionType t);
 
   /**
    * Compute the least upper bound of two types.
    */
   DartType getLeastUpperBound(
       TypeProvider typeProvider, DartType type1, DartType type2,
-      {dynamicIsBottom: false}) {
+      {bool dynamicIsBottom: false}) {
     // The least upper bound relation is reflexive.
     if (identical(type1, type2)) {
       return type1;
     }
     // The least upper bound of top and any type T is top.
     // The least upper bound of bottom and any type T is T.
     if (_isTop(type1, dynamicIsBottom: dynamicIsBottom) ||
         _isBottom(type2, dynamicIsBottom: dynamicIsBottom)) {
       return type1;
     }
@@ skipping 627 matching lines @@
 }
 
 bool _isBottom(DartType t, {bool dynamicIsBottom: false}) {
   return (t.isDynamic && dynamicIsBottom) || t.isBottom;
 }
 
 bool _isTop(DartType t, {bool dynamicIsBottom: false}) {
   // TODO(leafp): Document the rules in play here
   return (t.isDynamic && !dynamicIsBottom) || t.isObject;
 }