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

pkg/compiler/lib/src/common_elements.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.
 
 // TODO(sigmund): rename and move to common/elements.dart
 library dart2js.type_system;
 
 import 'common/names.dart' show Identifiers, Uris;
 import 'constants/values.dart';
 import 'elements/entities.dart';
@@ skipping 913 matching lines @@
 
   FunctionEntity get throwIndexOutOfRangeException =>
       _findHelperFunction('ioore');
 
   FunctionEntity get exceptionUnwrapper =>
       _findHelperFunction('unwrapException');
 
   FunctionEntity get throwRuntimeError =>
       _findHelperFunction('throwRuntimeError');
 
+  FunctionEntity get throwUnsupportedError =>
+      _findHelperFunction('throwUnsupportedError');
+
   FunctionEntity get throwTypeError => _findHelperFunction('throwTypeError');
 
   FunctionEntity get throwAbstractClassInstantiationError =>
       _findHelperFunction('throwAbstractClassInstantiationError');
 
   FunctionEntity _cachedCheckConcurrentModificationError;
   FunctionEntity get checkConcurrentModificationError =>
       _cachedCheckConcurrentModificationError ??=
           _findHelperFunction('checkConcurrentModificationError');
 
@@ skipping 322 matching lines @@
   // TODO(johnniwinther): Remove this when the resolver is removed.
   DartType getUnaliasedType(DartType type);
 
   /// Returns `true` if [member] a the synthetic getter `loadLibrary` injected
   /// on deferred libraries.
   bool isDeferredLoadLibraryGetter(MemberEntity member);
 
   /// Returns the metadata constants declared on [member].
   Iterable<ConstantValue> getMemberMetadata(MemberEntity member);
 }