IDR_THEME_TAB_BACKGROUND_INCOGNITO should not be defined on Mac.

chrome/browser/themes/browser_theme_pack.cc

 // 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.
 
 #include "chrome/browser/themes/browser_theme_pack.h"
 
 #include <limits>
 
 #include "base/files/file.h"
 #include "base/memory/ref_counted_memory.h"
@@ skipping 94 matching lines @@
   { PRS_THEME_FRAME_INACTIVE, IDR_THEME_FRAME_INACTIVE,
     "theme_frame_inactive" },
   { PRS_THEME_FRAME_INCOGNITO, IDR_THEME_FRAME_INCOGNITO,
     "theme_frame_incognito" },
   { PRS_THEME_FRAME_INCOGNITO_INACTIVE, IDR_THEME_FRAME_INCOGNITO_INACTIVE,
     "theme_frame_incognito_inactive" },
   { PRS_THEME_TOOLBAR, IDR_THEME_TOOLBAR,
     "theme_toolbar" },
   { PRS_THEME_TAB_BACKGROUND, IDR_THEME_TAB_BACKGROUND,
     "theme_tab_background" },
+#if !defined(OS_MACOSX)
   { PRS_THEME_TAB_BACKGROUND_INCOGNITO, IDR_THEME_TAB_BACKGROUND_INCOGNITO,
     "theme_tab_background_incognito" },
+#endif
   { PRS_THEME_TAB_BACKGROUND_V, IDR_THEME_TAB_BACKGROUND_V,
     "theme_tab_background_v"},
   { PRS_THEME_NTP_BACKGROUND, IDR_THEME_NTP_BACKGROUND,
     "theme_ntp_background" },
   { PRS_THEME_FRAME_OVERLAY, IDR_THEME_FRAME_OVERLAY,
     "theme_frame_overlay" },
   { PRS_THEME_FRAME_OVERLAY_INACTIVE, IDR_THEME_FRAME_OVERLAY_INACTIVE,
     "theme_frame_overlay_inactive" },
   { PRS_THEME_BUTTON_BACKGROUND, IDR_THEME_BUTTON_BACKGROUND,
     "theme_button_background" },
@@ skipping 1484 matching lines @@
                                            false,
                                            &bitmap_data)) {
       NOTREACHED() << "Unable to encode theme image for prs_id="
                    << prs_id << " for scale_factor=" << scale_factors_[i];
       break;
     }
     image_memory_[scaled_raw_id] =
         base::RefCountedBytes::TakeVector(&bitmap_data);
   }
 }