Add logic to exclude certain libraries from API doc.

pkg/dartdoc/lib/dartdoc.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.
 
 /**
  * To generate docs for a library, run this script with the path to an
  * entrypoint .dart file, like:
  *
  *     $ dart dartdoc.dart foo.dart
  *
@@ skipping 249 matching lines @@
 
   /**
    * Returns `true` if [library] is included in the generated documentation.
    */
   bool shouldIncludeLibrary(LibraryMirror library) {
     if (shouldLinkToPublicApi(library)) {
       return false;
     }
     var includeByDefault = true;
     String libraryName = displayName(library);
+    if (excludedLibraries.contains(libraryName)) {
+      return false;
+    }
     if (!includedLibraries.isEmpty) {
       includeByDefault = false;
-      if (includedLibraries.indexOf(libraryName) != -1) {
+      if (includedLibraries.contains(libraryName)) {
         return true;
       }
     }
-    if (excludedLibraries.indexOf(libraryName) != -1) {
-      return false;
-    }
     if (libraryName.startsWith('dart:')) {
       String suffix = libraryName.substring('dart:'.length);
       LibraryInfo info = LIBRARIES[suffix];
       if (info != null) {
         return info.documented && includeApi;
       }
     }
     return includeByDefault;
   }
 
@@ skipping 1568 matching lines @@
   final InterfaceMirror inheritedFrom;
 
   DocComment(this.text, [this.inheritedFrom = null]) {
     assert(text != null && !text.trim().isEmpty);
   }
 
   String get html => md.markdownToHtml(text);
 
   String toString() => text;
 }