Track emitted classes in incremental compiler.

dart/pkg/dart2js_incremental/lib/caching_compiler.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.
 
 part of dart2js_incremental;
 
 /// Do not call this method directly. It will be made private.
 // TODO(ahe): Make this method private.
 Future<Compiler> reuseCompiler(
     {DiagnosticHandler diagnosticHandler,
@@ skipping 127 matching lines @@
         ..nativeClasses.clear()
         ..nativeMethods.clear();
 
     backend.emitter.readTypeVariables.clear();
 
     backend.emitter.oldEmitter
         ..outputBuffers.clear()
         ..deferredConstants.clear()
         ..isolateProperties = null
         ..classesCollector = null
+        ..neededClasses.clear()
         ..outputClassLists.clear()
         ..nativeClasses.clear()
         ..mangledFieldNames.clear()
         ..mangledGlobalFieldNames.clear()
         ..recordedMangledNames.clear()
         ..additionalProperties.clear()
         ..clearCspPrecompiledNodes()
         ..elementDescriptors.clear();
 
     backend.emitter
         ..outputContainsConstantList = false;
 
     backend
         ..preMirrorsMethodCount = 0;
 
     if (reuseLibrary == null) {
       reuseLibrary = (LibraryElement library) {
         return new Future.value(
             library.isPlatformLibrary ||
             (packagesAreImmutable && library.isPackageLibrary));
       };
     }
     return compiler.libraryLoader.resetAsync(reuseLibrary).then((_) {
       oldTag.makeCurrent();
       return compiler;
     });
   }
 }