Remove factory body in *.fromEnvironment, and implement this same behavior

pkg/compiler/lib/src/kernel/elements.dart

 // Copyright (c) 2017, 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.
 
 /// Entity model for elements derived from Kernel IR.
 
 import '../elements/entities.dart';
 import '../elements/names.dart';
 import '../elements/types.dart';
 
@@ skipping 102 matching lines @@
 
   @override
   bool get isInstanceMember => false;
 
   @override
   bool get isStatic => false;
 
   @override
   bool get isTopLevel => false;
 
+  @override
+  bool get isFromEnvironmentConstructor => false;
+
   String get _kind => 'constructor';
 }
 
 class KGenerativeConstructor extends KConstructor {
   KGenerativeConstructor(int constructorIndex, KClass enclosingClass, Name name,
       ParameterStructure parameterStructure, {bool isExternal, bool isConst})
       : super(constructorIndex, enclosingClass, name, parameterStructure,
             isExternal: isExternal, isConst: isConst);
 
   @override
   bool get isFactoryConstructor => false;
 
   @override
   bool get isGenerativeConstructor => true;
 }
 
 class KFactoryConstructor extends KConstructor {
+  @override
+  final bool isFromEnvironmentConstructor;
+
   KFactoryConstructor(int memberIndex, KClass enclosingClass, Name name,
-      ParameterStructure parameterStructure, {bool isExternal, bool isConst})
+      ParameterStructure parameterStructure,
+      {bool isExternal, bool isConst, this.isFromEnvironmentConstructor})
       : super(memberIndex, enclosingClass, name, parameterStructure,
             isExternal: isExternal, isConst: isConst);
 
   @override
   bool get isFactoryConstructor => true;
 
   @override
   bool get isGenerativeConstructor => false;
 }
 
@@ skipping 74 matching lines @@
   final MemberEntity memberContext;
   final Entity executableContext;
   final FunctionType functionType;
 
   KLocalFunction(
       this.name, this.memberContext, this.executableContext, this.functionType);
 
   String toString() =>
       'local_function(${memberContext.name}.${name ?? '<anonymous>'})';
 }