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

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

 // Copyright (c) 2016, 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 entities;
 
 import '../common.dart';
 import '../universe/call_structure.dart' show CallStructure;
 
 /// Abstract interface for entities.
@@ skipping 119 matching lines @@
 /// Currently only [ConstructorElement] but later also kernel based Dart
 /// constructors and/or Dart-in-JS constructor-like properties.
 // TODO(johnniwinther): Remove factory constructors from the set of
 // constructors.
 abstract class ConstructorEntity extends FunctionEntity {
   /// Whether this is a generative constructor, possibly redirecting.
   bool get isGenerativeConstructor;
 
   /// Whether this is a factory constructor, possibly redirecting.
   bool get isFactoryConstructor;
+
+  /// Whether this is a `fromEnvironment` const constructor in `int`, `bool` or
+  /// `String`.
+  bool get isFromEnvironmentConstructor;
 }
 
 /// An entity that defines a local entity (memory slot) in generated code.
 ///
 /// Parameters, local variables and local functions (can) define local entity
 /// and thus implement [Local] through [LocalElement]. For non-element locals,
 /// like `this` and boxes, specialized [Local] classes are created.
 ///
 /// Type variables can introduce locals in factories and constructors
 /// but since one type variable can introduce different locals in different
@@ skipping 35 matching lines @@
   int get optionalParameters =>
       positionalParameters - requiredParameters + namedParameters.length;
 
   /// Returns the [CallStructure] corresponding to a call site passing all
   /// parameters both required and optional.
   CallStructure get callStructure {
     return new CallStructure(
         positionalParameters + namedParameters.length, namedParameters);
   }
 }