Adding support for sending horizonatal mouse wheel information in Chrome ASH on Windows 8.

ui/metro_viewer/metro_viewer_messages.h

 // Copyright 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.
 
 // Multiply-included message file, no include guard.
 
 #include <vector>
 
 #include "base/basictypes.h"
 #include "ipc/ipc_message_macros.h"
 #include "ui/events/event_constants.h"
 #include "ui/gfx/native_widget_types.h"
 #include "ui/metro_viewer/ime_types.h"
 
 #define IPC_MESSAGE_START MetroViewerMsgStart
 
 IPC_ENUM_TRAITS(ui::EventType)
 IPC_ENUM_TRAITS(ui::EventFlags)
 
 // Contains the parameters sent for a mousebutton message.
 IPC_STRUCT_BEGIN(MetroViewerHostMsg_MouseButtonParams)
 
   IPC_STRUCT_MEMBER(int32, x)
   IPC_STRUCT_MEMBER(int32, y)
   IPC_STRUCT_MEMBER(int32, extra)
   IPC_STRUCT_MEMBER(ui::EventType, event_type)
   IPC_STRUCT_MEMBER(uint32, flags)
   IPC_STRUCT_MEMBER(ui::EventFlags, changed_button)
+  IPC_STRUCT_MEMBER(bool, is_horizontal_wheel)
 
 IPC_STRUCT_END()
 
 // Messages sent from the viewer to the browser:
 
 // Inform the browser of the surface to target for compositing.
 IPC_MESSAGE_CONTROL1(MetroViewerHostMsg_SetTargetSurface,
                      gfx::NativeViewId /* target hwnd */)
 // Informs the browser that the mouse moved.
 IPC_MESSAGE_CONTROL3(MetroViewerHostMsg_MouseMoved,
@@ skipping 175 matching lines @@
   IPC_STRUCT_TRAITS_MEMBER(right)
   IPC_STRUCT_TRAITS_MEMBER(bottom)
 IPC_STRUCT_TRAITS_END()
 
 // Requests the viewer to update the document context such as attached
 // InputScopes and character bounds.
 IPC_MESSAGE_CONTROL2(
     MetroViewerHostMsg_ImeTextInputClientUpdated,
     std::vector<int32>,                           /* InputScope enums */
     std::vector<metro_viewer::CharacterBounds>)   /* character bounds */