Finish cleaning up analyzer warnings

pkg/compiler/lib/src/use_unused_api.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.
 
 /// This file use methods that aren't used by dart2js.dart, but that we wish to
 /// keep anyway. This might be general API that isn't currently in use,
 /// debugging aids, or API only used for testing (see TODO below).
 
 library dart2js.use_unused_api;
 
@@ skipping 11 matching lines @@
 import 'diagnostics/source_span.dart' as diagnostics;
 import 'elements/elements.dart' as elements;
 import 'elements/modelx.dart' as modelx;
 import 'elements/visitor.dart' as elements_visitor;
 import 'filenames.dart' as filenames;
 import 'inferrer/type_graph_inferrer.dart' as type_graph_inferrer;
 import 'io/location_provider.dart' as io;
 import 'io/source_map_builder.dart' as io;
 import 'js/js.dart' as js;
 import 'js_backend/js_backend.dart' as js_backend;
-import 'js_emitter/full_emitter/emitter.dart' as full;
-import 'js_emitter/js_emitter.dart' as js_emitter;
-import 'js_emitter/program_builder/program_builder.dart' as program_builder;
 import 'parser/partial_elements.dart'
     show PartialClassElement, PartialFunctionElement;
 import 'resolution/operators.dart' as operators;
 import 'resolution/semantic_visitor.dart' as semantic_visitor;
 import 'script.dart';
 import 'source_file_provider.dart' as source_file_provider;
 import 'ssa/nodes.dart' as ssa;
 import 'tree/tree.dart' as tree;
 import 'util/util.dart' as util;
 import 'world.dart';
@@ skipping 248 matching lines @@
   operators.UnaryOperator.fromKind(null);
   operators.BinaryOperator.fromKind(null);
   new semantic_visitor.BulkSendVisitor()..apply(null, null);
   new semantic_visitor.TraversalVisitor(null).apply(null, null);
   new semantic_visitor.BulkDeclarationVisitor().apply(null, null);
 }
 
 useDeferred([deferred_load.DeferredLoadTask task]) {
   task.dump();
 }