Fixes docgen build step on Windows.

utils/apidoc/docgen.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' : {
     'script_suffix%': '',
   },
   'conditions' : [
     ['OS=="win"', {
       'variables' : {
         'script_suffix': '.bat',
       },
     }],
   ],
   'targets': [
     {
       'target_name': 'docgen',
       'type': 'none',
       'dependencies': [
-        '../../utils/compiler/compiler.gyp:dart2js',
-        '../../runtime/dart-runtime.gyp:dart',
+        '../../create_sdk.gyp:create_sdk_internal',
         '../../pkg/pkg.gyp:pkg_packages',
+        '../../pkg/pkg_files.gyp:pkg_files_stamp',
       ],
       'includes': [
         '../../sdk/lib/core/corelib_sources.gypi',
       ],
       'actions': [
         {
           'action_name': 'run_docgen',
           # The 'inputs' list records the files whose timestamps are
           # compared to the files listed in 'outputs'.  If a file
           # 'outputs' doesn't exist or if a file in 'inputs' is newer
@@ skipping 24 matching lines @@
             '<(SHARED_INTERMEDIATE_DIR)/utils_wrapper.dart.snapshot',
             '<!@(["python", "../../tools/list_files.py", "\\.(css|ico|js|json|png|sh|txt|yaml|py)$", ".", "../../sdk/lib/_internal/dartdoc"])',
             '<!@(["python", "../../tools/list_files.py", "\\.dart$", ".", "../../sdk/lib", "../../runtime/lib", "../../runtime/bin"])',
             '../../sdk/bin/dart',
             '../../sdk/bin/dart.bat',
             '../../sdk/bin/dart2js',
             '../../sdk/bin/dart2js.bat',
             '../../sdk/bin/docgen',
             '../../sdk/bin/docgen.bat',
             '../../tools/only_in_release_mode.py',
+            '<(PRODUCT_DIR)/dart-sdk/README',
+            '<(SHARED_INTERMEDIATE_DIR)/pkg_files.stamp',
           ],
           'outputs': [
             '<(PRODUCT_DIR)/api_docs/docgen/index.json',
           ],
           'action': [
             'python',
             '../../tools/only_in_release_mode.py',
             '<@(_outputs)',
             '--',
-            '../../sdk/bin/dart',
-            '--package-root=<(PRODUCT_DIR)/packages',
-            '../../pkg/docgen/bin/docgen.dart',
+            '<(PRODUCT_DIR)/dart-sdk/bin/docgen<(script_suffix)',
             '--out=<(PRODUCT_DIR)/api_docs/docgen',
             '--include-sdk',
             '--no-include-dependent-packages',
             '--package-root=<(PRODUCT_DIR)/packages',
             '--exclude-lib=async_helper',
             '--exclude-lib=expect',
             '--exclude-lib=docgen',
             '../../pkg'
           ],
           'message': 'Running docgen: <(_action)',
         },
       ],
     }
   ],
 }