Generate API docs during build.

dart.gyp

 # 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.
 
 {
   'variables': {
     # These variables are used in the creation of the .vcproj file on
     # Windows.
     'cygwin_dir': 'third_party/cygwin',
   },
@@ skipping 87 matching lines @@
       'dependencies': [
         'utils/compiler/compiler.gyp:dart2js',
 
         # TODO(ahe): Remove dependencies on frog and frogsh, they are
         # just here to simplify
         # frog/scripts/buildbot_annotated_steps.py temporarily.
         'frog/dart-frog.gyp:frog',
         'frog/dart-frog.gyp:frogsh',
       ],
     },
+    {
+      'target_name': 'api_docs',
+      'type': 'none',
+      'dependencies': [
+        'utils/apidoc/apidoc.gyp:api_docs',
+      ],
+    }
   ],
 }