Use WebIDBKeyPath type in WebKit API, implement IndexedDBKeyPath type.

content/content_common.gypi

 # Copyright (c) 2012 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.
 
 {
   'dependencies': [
     '../base/base.gyp:base',
     '../build/temp_gyp/googleurl.gyp:googleurl',
     '../gpu/gpu.gyp:gles2_implementation',
     '../gpu/gpu.gyp:gpu_ipc',
@@ skipping 185 matching lines @@
     'common/gpu/media/gpu_video_decode_accelerator.h',
     'common/gpu/texture_image_transport_surface.h',
     'common/gpu/texture_image_transport_surface.cc',
     'common/handle_enumerator_win.cc',
     'common/handle_enumerator_win.h',
     'common/hi_res_timer_manager_posix.cc',
     'common/hi_res_timer_manager_win.cc',
     'common/hi_res_timer_manager.h',
     'common/indexed_db/indexed_db_key.cc',
     'common/indexed_db/indexed_db_key.h',
+    'common/indexed_db/indexed_db_key_path.cc',
+    'common/indexed_db/indexed_db_key_path.h',
     'common/indexed_db/indexed_db_key_range.cc',
     'common/indexed_db/indexed_db_key_range.h',
     'common/indexed_db/indexed_db_messages.h',
     'common/indexed_db/indexed_db_param_traits.cc',
     'common/indexed_db/indexed_db_param_traits.h',
     'common/indexed_db/indexed_db_dispatcher.cc',
     'common/indexed_db/indexed_db_dispatcher.h',
     'common/indexed_db/indexed_db_message_filter.cc',
     'common/indexed_db/indexed_db_message_filter.h',
     'common/indexed_db/proxy_webidbcursor_impl.cc',
@@ skipping 224 matching lines @@
         '../build/extract_from_cab.py',
         '..\\third_party\\directxsdk\\files\\Redist\\<(input)',
         '<(output)',
         '<(PRODUCT_DIR)',
         ],
       },
      ]
     }]
   ],
 }