Guarded shrink setting with ifdefs to make clear where it is used.

chrome/common/print_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 printing.
 // Multiply-included message file, hence no include guard.
 
 #include <string>
 #include <vector>
 
@@ skipping 235 matching lines @@
 
   // Size of the metafile data.
   IPC_STRUCT_MEMBER(uint32, data_size)
 
   // Cookie for the document to ensure correctness.
   IPC_STRUCT_MEMBER(int, document_cookie)
 
   // Page number.
   IPC_STRUCT_MEMBER(int, page_number)
 
+#if defined(OS_WIN) && !defined(WIN_PDF_METAFILE_FOR_PRINTING)
   // Shrink factor used to render this page.
   IPC_STRUCT_MEMBER(double, actual_shrink)
+#endif  // OS_WIN && !WIN_PDF_METAFILE_FOR_PRINTING
 
   // The size of the page the page author specified.
   IPC_STRUCT_MEMBER(gfx::Size, page_size)
 
   // The printable area the page author specified.
   IPC_STRUCT_MEMBER(gfx::Rect, content_area)
 IPC_STRUCT_END()
 
 // Parameters for the IPC message ViewHostMsg_ScriptedPrint
 IPC_STRUCT_BEGIN(PrintHostMsg_ScriptedPrint_Params)
@@ skipping 168 matching lines @@
 IPC_SYNC_MESSAGE_ROUTED0_0(PrintHostMsg_SetupScriptedPrintPreview)
 
 // Tell the browser to show the print preview, when the document is sufficiently
 // loaded such that the renderer can determine whether it is modifiable or not.
 IPC_MESSAGE_ROUTED1(PrintHostMsg_ShowScriptedPrintPreview,
                     bool /* is_modifiable */)
 
 // Notify the browser that the PDF in the initiator renderer has disabled print
 // scaling option.
 IPC_MESSAGE_ROUTED0(PrintHostMsg_PrintPreviewScalingDisabled)