Add NativeEnqueuer to work with the Enqueuer.

lib/compiler/implementation/compiler.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 dart2js;
 
 /**
  * If true, print a warning for each method that was resolved, but not
  * compiled.
  */
@@ skipping 56 matching lines @@
       : this.constantSystem = constantSystem;
 
   void enqueueAllTopLevelFunctions(LibraryElement lib, Enqueuer world) {
     lib.forEachExport((Element e) {
       if (e.isFunction()) world.addToWorkList(e);
     });
   }
 
   abstract void enqueueHelpers(Enqueuer world);
   abstract void codegen(WorkItem work);
-  abstract void processNativeClasses(Enqueuer world,
-                                     Collection<LibraryElement> libraries);
+
+  // The backend determines the native resolution enqueuer so tools like
+  // dart2dart can ignore the native classes.
+  abstract NativeEnqueuer nativeResolutionEnqueuer(world);
+  abstract NativeEnqueuer nativeCodegenEnqueuer(world);
+
   abstract void assembleProgram();
   abstract List<CompilerTask> get tasks;
 
   // TODO(ahe,karlklose): rename this?
   void dumpInferredTypes() {}
 
   ItemCompilationContext createItemCompilationContext() {
     return new ItemCompilationContext();
   }
 
@@ skipping 388 matching lines @@
       reportFatalError('Could not find $MAIN', mainApp);
     } else {
       if (!main.isFunction()) reportFatalError('main is not a function', main);
       FunctionElement mainMethod = main;
       FunctionSignature parameters = mainMethod.computeSignature(this);
       parameters.forEachParameter((Element parameter) {
         reportFatalError('main cannot have parameters', parameter);
       });
     }
 
+    enqueuer.resolution.nativeEnqueuer =
+        backend.nativeResolutionEnqueuer(enqueuer.resolution);
+    enqueuer.codegen.nativeEnqueuer =
+        backend.nativeCodegenEnqueuer(enqueuer.codegen);
+
     log('Resolving...');
     phase = PHASE_RESOLVING;
     backend.enqueueHelpers(enqueuer.resolution);
     processQueue(enqueuer.resolution, main);
     log('Resolved ${enqueuer.resolution.resolvedElements.length} elements.');
 
     if (compilationFailed) return;
 
     log('Inferring types...');
     typesTask.onResolutionComplete(main);
 
     // TODO(ahe): Remove this line. Eventually, enqueuer.resolution
     // should know this.
     world.populate();
 
     log('Compiling...');
     phase = PHASE_COMPILING;
     processQueue(enqueuer.codegen, main);
     log('Compiled ${codegenWorld.generatedCode.length} methods.');
 
     if (compilationFailed) return;
 
     backend.assembleProgram();
 
     checkQueues();
   }
 
   void processQueue(Enqueuer world, Element main) {
-    backend.processNativeClasses(world, libraries.values);
+    world.nativeEnqueuer.processNativeClasses(libraries.values);
     world.addToWorkList(main);
     progress.reset();
     world.forEach((WorkItem work) {
       withCurrentElement(work.element, () => work.run(this, world));
     });
     world.queueIsClosed = true;
     if (compilationFailed) return;
     assert(world.checkNoEnqueuedInvokedInstanceMethods());
     if (DUMP_INFERRED_TYPES && phase == PHASE_COMPILING) {
       backend.dumpInferredTypes();
@@ skipping 336 matching lines @@
   // TODO(johnniwinther): Use [spannable] and [message] to provide better
   // information on assertion errors.
   if (condition is Function){
     condition = condition();
   }
   if (!condition && message != null) {
     print('assertion failed: $message');
   }
   return spannable != null && condition;
 }