Eliminate multi-callback structure for LibraryLoader.

tests/compiler/dart2js/exit_code_test.dart

 // Copyright (c) 2013, 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.
 
 // Test the exit code of dart2js in case of exceptions, errors, warnings, etc.
 
 import 'dart:async';
 import 'dart:io' show Platform;
 
 import 'package:async_helper/async_helper.dart';
@@ skipping 56 matching lines @@
   @override
   ResolverTask createResolverTask() {
     return new TestResolver(this, backend.constantCompilerTask);
   }
 
   Future<bool> run(Uri uri) {
     test('Compiler.run');
     return super.run(uri);
   }
 
-  Future onLibraryScanned(LibraryElement element, LibraryLoader loader) {
-    test('Compiler.onLibraryScanned');
-    return super.onLibraryScanned(element, loader);
-  }
-
-  Future onLibrariesLoaded(LoadedLibraries loadedLibraries) {
-    test('Compiler.onLibrariesLoaded');
-    return super.onLibrariesLoaded(loadedLibraries);
+  LoadedLibraries processLoadedLibraries(LoadedLibraries loadedLibraries) {
+    test('Compiler.processLoadedLibraries');
+    return super.processLoadedLibraries(loadedLibraries);
   }
 
   test(String marker) {
     if (marker == testMarker) {
       switch (testType) {
         case 'assert':
           onTest(testMarker, testType);
           assert(false);
           break;
         case 'invariant':
@@ skipping 194 matching lines @@
       'error': 1,
       'internalError': 253,
     };
   }
 
   const beforeRun = false;
   const duringRun = true;
   final tests = {
     'Compiler': beforeRun,
     'Compiler.run': beforeRun,
-    'Compiler.onLibraryScanned': beforeRun,
-    'Compiler.onLibrariesLoaded': beforeRun,
+    'Compiler.processLoadedLibraries': beforeRun,
     'ScannerTask.scanElements': duringRun,
     'Compiler.withCurrentElement': duringRun,
     'Compiler.analyzeElement': duringRun,
     'Compiler.codegen': duringRun,
     'ResolverTask.computeClassMembers': duringRun,
   };
   int totalExpectedErrors = 0;
 
   asyncTest(() async {
     for (String marker in tests.keys) {
       var expected = _expectedExitCode(beforeRun: tests[marker]);
       totalExpectedErrors += expected.length;
       await testExitCodes(marker, expected, []);
 
       expected =
           _expectedExitCode(beforeRun: tests[marker], fatalWarnings: true);
       totalExpectedErrors += expected.length;
       await testExitCodes(marker, expected, ['--fatal-warnings']);
     }
 
     Expect.equals(totalExpectedErrors, checkedResults);
   });
 }