Remove more type casts

pkg/analyzer/lib/source/embedder.dart

 // Copyright (c) 2015, 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.
 
 library analyzer.source.embedder;
 
 import 'dart:collection' show HashMap;
 import 'dart:core' hide Resource;
 
 import 'package:analyzer/file_system/file_system.dart';
@@ skipping 193 matching lines @@
     SdkLibraryImpl library = new SdkLibraryImpl(shortName);
     library.path = libPath;
     (dartSdk as EmbedderSdk)._librariesMap.setLibrary(name, library);
   }
 
   void _processEmbedderYaml(Folder libDir, YamlMap map) {
     YamlNode embedded_libs = map[_EMBEDDED_LIB_MAP_KEY];
     if (embedded_libs == null) {
       return;
     }
-    if (embedded_libs is! YamlMap) {
-      return;
+    if (embedded_libs is YamlMap) {
+      embedded_libs.forEach((k, v) => _processEmbeddedLibs(k, v, libDir));
     }
-    (embedded_libs as YamlMap)
-        .forEach((k, v) => _processEmbeddedLibs(k, v, libDir));
   }
 }
 
 /// Given a packageMap, check in each package's lib directory for the
 /// existence of an `_embedder.yaml` file. If the file contains a top level
 /// YamlMap, it will be added to the [embedderYamls] map.
 class EmbedderYamlLocator {
   static const String EMBEDDER_FILE_NAME = '_embedder.yaml';
 
   // Map from package's library directory to the parsed
@@ skipping 60 matching lines @@
   String _readEmbedderYaml(Folder libDir) {
     File file = libDir.getChild(EMBEDDER_FILE_NAME);
     try {
       return file.readAsStringSync();
     } on FileSystemException {
       // File can't be read.
       return null;
     }
   }
 }