fix #25573, add option to disable implicit dynamic

pkg/analyzer/lib/src/generated/engine.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 analyzer.src.generated.engine;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 1292 matching lines @@
 
   /**
    * A flag indicating whether implicit casts are allowed in [strongMode]
    * (they are always allowed in Dart 1.0 mode).
    *
    * This option is experimental and subject to change.
    */
   bool implicitCasts = true;
 
   /**
+   * A flag indicating whether implicit dynamic type is allowed, on by default.
+   *
+   * This flag can be used without necessarily enabling [strongMode], but it is
+   * designed with strong mode's type inference in mind. Without type inference,
+   * it will raise many errors. Also it does not provide type safety without
+   * strong mode.
+   *
+   * This option is experimental and subject to change.
+   */
+  bool implicitDynamic = true;
+
+  /**
    * Initialize a newly created set of analysis options to have their default
    * values.
    */
   AnalysisOptionsImpl();
 
   /**
    * Initialize a newly created set of analysis options to have the same values
    * as those in the given set of analysis [options].
    */
   AnalysisOptionsImpl.from(AnalysisOptions options) {
@@ skipping 11 matching lines @@
     hint = options.hint;
     incremental = options.incremental;
     incrementalApi = options.incrementalApi;
     incrementalValidation = options.incrementalValidation;
     lint = options.lint;
     preserveComments = options.preserveComments;
     strongMode = options.strongMode;
     if (options is AnalysisOptionsImpl) {
       strongModeHints = options.strongModeHints;
       implicitCasts = options.implicitCasts;
+      implicitDynamic = options.implicitDynamic;
     }
     trackCacheDependencies = options.trackCacheDependencies;
   }
 
   bool get analyzeFunctionBodies {
     if (identical(analyzeFunctionBodiesPredicate, _analyzeAllFunctionBodies)) {
       return true;
     } else if (identical(
         analyzeFunctionBodiesPredicate, _analyzeNoFunctionBodies)) {
       return false;
@@ skipping 1240 matching lines @@
    * The data that was created from the source.
    */
   final E data;
 
   /**
    * Initialize a newly created holder to associate the given [data] with the
    * given [modificationTime].
    */
   TimestampedData(this.modificationTime, this.data);
 }