Make scrollAnimatorEnabled work on Mac like it does on other platforms

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 <stddef.h>
 #include <stdint.h>
 
@@ skipping 535 matching lines @@
   IPC_STRUCT_MEMBER(gfx::Size, max_size)
 IPC_STRUCT_END()
 
 #if defined(OS_MACOSX)
 IPC_STRUCT_BEGIN(ViewMsg_UpdateScrollbarTheme_Params)
   IPC_STRUCT_MEMBER(float, initial_button_delay)
   IPC_STRUCT_MEMBER(float, autoscroll_button_delay)
   IPC_STRUCT_MEMBER(bool, jump_on_track_click)
   IPC_STRUCT_MEMBER(blink::ScrollerStyle, preferred_scroller_style)
   IPC_STRUCT_MEMBER(bool, redraw)
-  IPC_STRUCT_MEMBER(bool, scroll_animation_enabled)
   IPC_STRUCT_MEMBER(blink::WebScrollbarButtonsPlacement, button_placement)
 IPC_STRUCT_END()
 #endif
 
 // Messages sent from the browser to the renderer.
 
 #if defined(OS_ANDROID)
 // Tells the renderer to cancel an opened date/time dialog.
 IPC_MESSAGE_ROUTED0(ViewMsg_CancelDateTimeDialog)
 
@@ skipping 768 matching lines @@
 // Instructs the browser to start plugin IME.
 IPC_MESSAGE_ROUTED0(ViewHostMsg_StartPluginIme)
 
 // Receives content of a web page as plain text.
 IPC_MESSAGE_ROUTED1(ViewMsg_GetRenderedTextCompleted, std::string)
 #endif
 
 // Adding a new message? Stick to the sort order above: first platform
 // independent ViewMsg, then ifdefs for platform specific ViewMsg, then platform
 // independent ViewHostMsg, then ifdefs for platform specific ViewHostMsg.