Introduces the new syntax for deferred loading

sdk/lib/_internal/compiler/implementation/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 1538 matching lines @@
     if (element == disableTreeShakingMarker) {
       compiler.disableTypeInferenceForMirrors = true;
       isTreeShakingDisabled = true;
       typeVariableHandler.onTreeShakingDisabled(enqueuer);
     } else if (element == preserveNamesMarker) {
       mustPreserveNames = true;
     } else if (element == preserveMetadataMarker) {
       mustRetainMetadata = true;
     } else if (element == getIsolateAffinityTagMarker) {
       needToInitializeIsolateAffinityTag = true;
+    } else if (element.isDeferredLoaderFunction()) {
+      // TODO(sigurdm): Create a function registerLoadLibraryAccess.
+      if (compiler.loadLibraryFunction == null) {
+        compiler.loadLibraryFunction = compiler.findHelper("_load");
+        enqueueInResolution(compiler.loadLibraryFunction,
+                            compiler.globalDependencies);
+      }
     }
     customElementsAnalysis.registerStaticUse(element, enqueuer);
   }
 
   /// Called when [:const Symbol(name):] is seen.
   void registerConstSymbol(String name, TreeElements elements) {
     symbolsUsed.add(name);
     if (name.endsWith('=')) {
       symbolsUsed.add(name.substring(0, name.length - 1));
     }
@@ skipping 348 matching lines @@
     copy(constant.values);
     copy(constant.protoValue);
     copy(constant);
   }
 
   void visitConstructed(ConstructedConstant constant) {
     copy(constant.fields);
     copy(constant);
   }
 }