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

pkg/compiler/lib/src/kernel/element_map_impl.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.
 
 library dart2js.kernel.element_map;
 
 import 'package:kernel/ast.dart' as ir;
 import 'package:kernel/clone.dart';
 import 'package:kernel/type_algebra.dart';
 
@@ skipping 252 matching lines @@
       bool isExternal = node.isExternal;
 
       ir.FunctionNode functionNode;
       if (node is ir.Constructor) {
         functionNode = node.function;
         constructor = new KGenerativeConstructor(memberIndex, enclosingClass,
             name, _getParameterStructure(functionNode),
             isExternal: isExternal, isConst: node.isConst);
       } else if (node is ir.Procedure) {
         functionNode = node.function;
+        bool isFromEnvironment = isExternal &&
+            name.text == 'fromEnvironment' &&
+            const ['int', 'bool', 'String'].contains(enclosingClass.name);
         constructor = new KFactoryConstructor(memberIndex, enclosingClass, name,
             _getParameterStructure(functionNode),
-            isExternal: isExternal, isConst: node.isConst);
+            isExternal: isExternal,
+            isConst: node.isConst,
+            isFromEnvironmentConstructor: isFromEnvironment);
       } else {
         // TODO(johnniwinther): Convert `node.location` to a [SourceSpan].
         throw new SpannableAssertionFailure(
             NO_LOCATION_SPANNABLE, "Unexpected constructor node: ${node}.");
       }
       _memberList.add(new _ConstructorData(node, functionNode));
       return constructor;
     });
   }
 
@@ skipping 1217 matching lines @@
     return node.isExternal &&
         !elementMap.isForeignLibrary(node.enclosingLibrary);
   }
 
   @override
   bool isJsInteropMember(MemberEntity element) {
     // TODO(johnniwinther): Compute this.
     return false;
   }
 }