Add CSS variables feature flag to chrome://flags.

content/common/view_messages.h

 // 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.
 
 // IPC messages for page rendering.
 // Multiply-included message file, hence no include guard.
 
 #include "base/process.h"
 #include "base/shared_memory.h"
 #include "content/common/content_export.h"
@@ skipping 192 matching lines @@
   IPC_STRUCT_TRAITS_MEMBER(accelerated_video_enabled)
   IPC_STRUCT_TRAITS_MEMBER(memory_info_enabled)
   IPC_STRUCT_TRAITS_MEMBER(fullscreen_enabled)
   IPC_STRUCT_TRAITS_MEMBER(allow_displaying_insecure_content)
   IPC_STRUCT_TRAITS_MEMBER(allow_running_insecure_content)
   IPC_STRUCT_TRAITS_MEMBER(enable_scroll_animator)
   IPC_STRUCT_TRAITS_MEMBER(visual_word_movement_enabled)
   IPC_STRUCT_TRAITS_MEMBER(password_echo_enabled)
   IPC_STRUCT_TRAITS_MEMBER(css_regions_enabled)
   IPC_STRUCT_TRAITS_MEMBER(css_shaders_enabled)
+  IPC_STRUCT_TRAITS_MEMBER(css_variables_enabled)
   IPC_STRUCT_TRAITS_MEMBER(device_supports_touch)
   IPC_STRUCT_TRAITS_MEMBER(device_supports_mouse)
 #if !defined(WEBCOMPOSITOR_OWNS_SETTINGS)
   IPC_STRUCT_TRAITS_MEMBER(threaded_animation_enabled)
   IPC_STRUCT_TRAITS_MEMBER(partial_swap_enabled)
   IPC_STRUCT_TRAITS_MEMBER(per_tile_painting_enabled)
 #endif
   IPC_STRUCT_TRAITS_MEMBER(default_tile_width)
   IPC_STRUCT_TRAITS_MEMBER(default_tile_height)
   IPC_STRUCT_TRAITS_MEMBER(max_untiled_layer_width)
@@ skipping 1938 matching lines @@
 // (according to the value of is_hung). The browser can give the user the
 // option of killing the plugin.
 IPC_MESSAGE_ROUTED3(ViewHostMsg_PepperPluginHung,
                     int /* plugin_child_id */,
                     FilePath /* path */,
                     bool /* is_hung */)
 
 // Screen was rotated. Dispatched to the onorientationchange javascript API.
 IPC_MESSAGE_ROUTED1(ViewMsg_OrientationChangeEvent,
                     int /* orientation */)