Extract create_sdk build rule to own file to avoid cycle.

dart/site/try/build_try.gyp

 # Copyright (c) 2014, 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
 
 {
   'targets': [
     {
       'target_name': 'try_site',
       'type': 'none',
       'dependencies': [
         '../../runtime/dart-runtime.gyp:dart',
-        # Concern: there should really be a dependency on
-        # ../../dart.gyp:create_sdk, but this is reported as a cycle by GYP.
+        '../../create_sdk.gyp:create_sdk',
       ],
       'variables': {
         'try_dart_static_files': [
           'index.html',
           'dartlang-style.css',
           'iframe.html',
           'iframe.js',
           'dart-icon.png', # iOS icon.
           'dart-iphone5.png', # iPhone 5 splash screen.
           'dart-icon-196px.png', # Android icon.
@@ skipping 88 matching lines @@
           'files': [
             'app.yaml',
             '<@(try_dart_static_files)',
             '<(SHARED_INTERMEDIATE_DIR)/nossl.appcache',
           ],
         },
       ],
     },
   ],
 }