Add PrintedPage::GetCenteredPageContentRect so Mac and Win can share code.

printing/printed_document_mac.cc

 // Copyright (c) 2009 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.
 
 #include "printing/printed_document.h"
 
 #import <ApplicationServices/ApplicationServices.h>
 #import <CoreFoundation/CoreFoundation.h>
 
 #include "base/logging.h"
 #include "base/scoped_cftyperef.h"
 #include "printing/page_number.h"
 #include "printing/printed_page.h"
 
 namespace printing {
 
 void PrintedDocument::RenderPrintedPage(
     const PrintedPage& page, gfx::NativeDrawingContext context) const {
 #ifndef NDEBUG
   {
     // Make sure the page is from our list.
     AutoLock lock(lock_);
     DCHECK(&page == mutable_.pages_.find(page.page_number() - 1)->second.get());
   }
 #endif
 
   const printing::PageSetup& page_setup(
       immutable_.settings_.page_setup_device_units());
-  gfx::Rect target_rect = page.page_content_rect();
-  const gfx::Rect& physical_size = page_setup.physical_size();
-  // http://dev.w3.org/csswg/css3-page/#positioning-page-box
-  if (physical_size.width() > page.page_size().width()) {
-    int diff = physical_size.width() - page.page_size().width();
-    target_rect.set_x(target_rect.x() + diff / 2);
-  }
-  if (physical_size.height() > page.page_size().height()) {
-    int diff = physical_size.height() - page.page_size().height();
-    target_rect.set_y(target_rect.y() + diff / 2);
-  }
+  gfx::Rect content_area;
+  page.GetCenteredPageContentRect(page_setup.physical_size(), &content_area);
 
   const printing::NativeMetafile* metafile = page.native_metafile();
   // Each NativeMetafile is a one-page PDF, and pages use 1-based indexing.
   const int page_number = 1;
-  metafile->RenderPage(page_number, context, target_rect.ToCGRect(),
+  metafile->RenderPage(page_number, context, content_area.ToCGRect(),
                        true, false, false, false);
 
   // TODO(stuartmorgan): Print the header and footer.
 }
 
 }  // namespace printing