Eliminate multi-callback structure for LibraryLoader.

pkg/compiler/lib/src/kernel/kernel.dart

 // Copyright (c) 2016, 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.md file.
 
 import 'dart:async';
 import 'dart:collection' show Queue;
 
 import 'package:kernel/ast.dart' as ir;
 import 'package:kernel/verifier.dart' show CheckParentPointers;
 
@@ skipping 19 matching lines @@
         ExportElement,
         FieldElement,
         FunctionElement,
         ImportElement,
         LibraryElement,
         LocalFunctionElement,
         MetadataAnnotation,
         MixinApplicationElement,
         TypeVariableElement;
 import '../elements/modelx.dart' show ErroneousFieldElementX;
+import '../library_loader.dart' show LoadedLibraries;
 import '../tree/tree.dart' show FunctionExpression, Node;
 import 'constant_visitor.dart';
 import 'kernel_visitor.dart' show IrFunction, KernelVisitor;
 
 typedef void WorkAction();
 
 class WorkItem {
   final Element element;
   final WorkAction action;
 
@@ skipping 85 matching lines @@
       ClassElement cls = element.enclosingClass;
       if (cls != null && cls.isMixinApplication) {
         MixinApplicationElement mixinApplication = cls;
         element = mixinApplication.mixin;
       }
       irLibrary = libraryToIr(element.library);
     }
     return new ir.Name(name, irLibrary);
   }
 
   Future<ir.Library> loadLibrary(Uri uri) async {

[Siggi Cherem (dart-lang), 2017/03/24 17:40:27]

it appears this method is never called, so we can probably delete it and remove
the dependency above :)

[Emily Fortuna, 2017/03/24 18:30:19]

ah good point!

-    return libraryToIr(await compiler.libraryLoader.loadLibrary(uri));
+    LoadedLibraries libraries = await compiler.libraryLoader.loadLibrary(uri);
+    await compiler.processLoadedLibraries(libraries);
+    return libraryToIr(libraries.rootLibrary);
   }
 
   ir.Library libraryToIr(LibraryElement library) {
     library = library.declaration;
     return libraries.putIfAbsent(library, () {
       String name = library.hasLibraryName ? library.libraryName : null;
       ir.Library libraryNode = new ir.Library(library.canonicalUri,
           name: name, classes: null, procedures: null, fields: null);
       addWork(library, () {
         Queue<ir.Class> classes = new Queue<ir.Class>();
@@ skipping 627 matching lines @@
 }
 
 class ConstructorTarget {
   final ConstructorElement element;
   final ResolutionDartType type;
 
   ConstructorTarget(this.element, this.type);
 
   String toString() => "ConstructorTarget($element, $type)";
 }