Split dart_api.h into multiple parts:

samples/sample_extension/sample_extension.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.
 
 {
   'targets': [
     {
       'target_name': 'sample_extension',
       'type': 'shared_library',
       'dependencies': [
         '../../runtime/dart-runtime.gyp:dart',
       ],
       'include_dirs': [
-        '../../runtime/include',
+        '../../runtime',
       ],
       'sources': [
         'sample_extension.cc',
         'sample_extension_dllmain_win.cc',
       ],
       'defines': [
         'DART_SHARED_LIB',
       ],
       'conditions': [
         ['OS=="win"', {
@@ skipping 11 matching lines @@
         }],
         ['OS=="linux"', {
           'cflags': [
             '-fPIC',
           ],
         }],
       ],
     },
   ],
 }