Support foreigns as external.

pkg/compiler/lib/src/js_backend/backend.dart

 // Copyright (c) 2012, 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.
 
 part of js_backend;
 
 const VERBOSE_OPTIMIZER_HINTS = false;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked = new Set<HInstruction>();
@@ skipping 624 matching lines @@
 
   ConstantSystem get constantSystem => constants.constantSystem;
 
   /// Returns constant environment for the JavaScript interpretation of the
   /// constants.
   JavaScriptConstantCompiler get constants {
     return constantCompilerTask.jsConstantCompiler;
   }
 
   FunctionElement resolveExternalFunction(FunctionElement element) {
+    if (isForeign(element)) return element;
     return patchResolverTask.measure(() {
       return patchResolverTask.resolveExternalFunction(element);
     });
   }
 
   // TODO(karlklose): Split into findHelperFunction and findHelperClass and
   // add a check that the element has the expected kind.
   Element findHelper(String name) => find(jsHelperLibrary, name);
   Element findInterceptor(String name) => find(interceptorsLibrary, name);
 
@@ skipping 2321 matching lines @@
   }
 }
 
 /// Records that [constant] is used by the element behind [registry].
 class Dependency {
   final ConstantValue constant;
   final Element annotatedElement;
 
   const Dependency(this.constant, this.annotatedElement);
 }