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

pkg/compiler/lib/src/js_backend/patch_resolver.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 dart2js.js_backend.patch_resolver;
 
 import '../common.dart';
 import '../common/resolution.dart' show Resolution;
 import '../common/tasks.dart' show CompilerTask;
 import '../compiler.dart' show Compiler;
@@ skipping 16 matching lines @@
 
   FunctionElement resolveExternalFunction(FunctionElementX element) {
     if (element.isPatched) {
       FunctionElementX patch = element.patch;
       reporter.withCurrentElement(patch, () {
         patch.computeType(resolution);
       });
       checkMatchingPatchSignatures(element, patch);
       element = patch;
     } else {
+      if (element.isConstructor) {
+        // Note: currently we allow a couple external methods without a patch,
+        // namely the *.fromEnvironment const constructors in int, bool, and
+        // String.  In the future we might also represent native DOM methods in
+        // dart:html this way.
+        ConstructorElementX constructor = element;
+        if (constructor.isFromEnvironmentConstructor) return element;
+      }
       reporter.reportErrorMessage(
           element, MessageKind.PATCH_EXTERNAL_WITHOUT_IMPLEMENTATION);
     }
     return element;
   }
 
   void checkMatchingPatchParameters(FunctionElement origin,
       List<Element> originParameters, List<Element> patchParameters) {
     bool isUnnamedListConstructor = origin is ConstructorElement &&
         compiler.commonElements.isUnnamedListConstructor(origin);
@@ skipping 129 matching lines @@
           'originParameterCount': originSignature.optionalParameterCount,
           'patchParameterCount': patchSignature.optionalParameterCount
         });
       });
     } else {
       checkMatchingPatchParameters(origin, originSignature.optionalParameters,
           patchSignature.optionalParameters);
     }
   }
 }