Include sync.pb.h in sync_data.h.

extensions/extensions.gyp

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
     {
@@ skipping 137 matching lines @@
     {
       'target_name': 'extensions_browser',
       'type': 'static_library',
       'dependencies': [
         'extensions_common',
         # TODO(jamescook|derat): Pull strings into extensions module.
         '../chrome/chrome_resources.gyp:chrome_strings',
         '../chrome/common/extensions/api/api.gyp:api',
         '../content/content.gyp:content_browser',
         '../skia/skia.gyp:skia',
+        # Declaring a dependency on sync because extensions_browser depends on
+        # browser_extensions, which depends on sync. We cannot simply declare a
+        # dependency on browser_extensions because that would create a cycle
+        # (browser_extension already depends on extensions_browser).

[Nico, 2014/03/07 19:13:00]

Same question as above.

[maniscalco, 2014/03/07 23:44:37]

No longer needed!

+         '../sync/sync.gyp:sync',
       ],
       'include_dirs': [
         '..',
         '<(INTERMEDIATE_DIR)',
         # Needed to access generated API headers.
         '<(SHARED_INTERMEDIATE_DIR)',
         # Needed for grit.
         '<(SHARED_INTERMEDIATE_DIR)/chrome',
       ],
       'sources': [
@@ skipping 92 matching lines @@
         'common/test_util.cc',
         'common/test_util.h',
         'common/value_builder.cc',
         'common/value_builder.h',
       ],
       # Disable c4267 warnings until we fix size_t to int truncations.
       'msvs_disabled_warnings': [ 4267, ],
     },
   ]
 }