clang/win: Let remaining chromium_code targets build with -Wextra.

ui/gfx/gdi_util.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 "ui/gfx/gdi_util.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 115 matching lines @@
     rv = ::StretchDIBits(hdc,
                          dest_x, dest_h + dest_y - 1, dest_w, -dest_h,
                          src_x, bitmap_h - src_y + 1, src_w, -src_h,
                          pixels, bitmap_info, DIB_RGB_COLORS, SRCCOPY);
   } else {
     rv = ::StretchDIBits(hdc,
                          dest_x, dest_y, dest_w, dest_h,
                          src_x, bottom_up_src_y, src_w, src_h,
                          pixels, bitmap_info, DIB_RGB_COLORS, SRCCOPY);
   }
-  DCHECK(rv != GDI_ERROR);
+  DCHECK(rv != static_cast<int>(GDI_ERROR));
 }
 
 }  // namespace gfx