Gtk: Change NULL to nullptr

chrome/browser/ui/libgtkui/skia_utils_gtk.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/ui/libgtkui/skia_utils_gtk.h"
 
 #include <gdk/gdk.h>
 
 #include "base/logging.h"
 #include "third_party/skia/include/core/SkBitmap.h"
@@ skipping 68 matching lines @@
     }
   } else {
     NOTREACHED();
   }
 
   return ret;
 }
 
 GdkPixbuf* GdkPixbufFromSkBitmap(const SkBitmap& bitmap) {
   if (bitmap.isNull())
-    return NULL;
+    return nullptr;
 
   SkAutoLockPixels lock_pixels(bitmap);
 
   int width = bitmap.width();
   int height = bitmap.height();
 
   GdkPixbuf* pixbuf =
       gdk_pixbuf_new(GDK_COLORSPACE_RGB,  // The only colorspace gtk supports.
                      TRUE,                // There is an alpha channel.
                      8, width, height);
@@ skipping 20 matching lines @@
         divided[i + 3] = alpha;
       }
       i += kBytesPerPixel;
     }
   }
 
   return pixbuf;
 }
 
 }  // namespace libgtkui