Allow to have a transparent UA dependent background.

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 783 matching lines @@
 // Changes the text direction of the currently selected input field (if any).
 IPC_MESSAGE_ROUTED1(ViewMsg_SetTextDirection,
                     blink::WebTextDirection /* direction */)
 
 // Tells the renderer to clear the focused element (if any).
 IPC_MESSAGE_ROUTED0(ViewMsg_ClearFocusedElement)
 
 // Make the RenderView background transparent or opaque.
 IPC_MESSAGE_ROUTED1(ViewMsg_SetBackgroundOpaque, bool /* opaque */)
 
+// Change the RenderView background color.
+IPC_MESSAGE_ROUTED1(ViewMsg_SetBackgroundColor, uint32_t /* SKcolorARGB */)
+
 // Used to tell the renderer not to add scrollbars with height and
 // width below a threshold.
 IPC_MESSAGE_ROUTED1(ViewMsg_DisableScrollbarsForSmallWindows,
                     gfx::Size /* disable_scrollbar_size_limit */)
 
 // Activate/deactivate the RenderView (i.e., set its controls' tint
 // accordingly, etc.).
 IPC_MESSAGE_ROUTED1(ViewMsg_SetActive,
                     bool /* active */)
 
@@ skipping 522 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.